-Chemical change- new substance is made, could be a precipitate- a solid formed by the settling of a liquid mixture, transfer of energy, change in color, or production of gas

-something new is formed with new physical and chemical properties (known as chemical reaction)

-in a reaction there are reactants which form products

-During any chemical reaction, the mass of the products is always equal to the mass of the reactants

-intensive property- does not depend on how much matter in a sample, you get the property regardless of the type of matter (flammability, malleability)

-extensive property- depends on how much matter you have in a sample to get the property

(mass, volume)

Law of Conservation

-Matter cannot be created or destroyed but changed from form to form

-the reactants and products of a reaction have the same mass

Textbook reading- Chapter 4, sections 1-3

Text next lecture- Chapters 1, section 3, Chapter 2, sections 1-4, and Chapter 4 sections 1-3

Wizard of oz

Maryland facts

Military facts

Atoms- smallest particle of an element that retains its identity in a chemical reaction, smallest whole part of all matter

What do we know about atoms?

John Dalton- father of Atomic Theory

5 parts of Atomic Theory

All elements are made of atoms
All the atoms of an element are the same
1. Some may not be the same- they are called isotopes and can have different masses
Atoms of different elements can be chemically or physically combined to make compounds
Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of one element are never changed into atoms of a different element because of a chemical reaction

Atoms are indivisible and indestructible- we can split them up, they are made of electrons that can move around to different atoms
1. This is what Democritus originally thought about atoms, but it wasn't scientifically supported as it was not based on the scientific method

-individual atoms can be seen through scanning tunneling microscopes

-The physical and chemical properties of atoms are determined by subatomic particles

-Proton

-Neutron

J.J Thomson

-Electron, discovered in 1897 by English physicist J.J Thomson

-J.J Thomson used experiments that involved the passing of electric currents through a glass tube

-each end had an electrode that gave off electricity

-one electrode, the anode, was positively charged

-the other electrode, the cathode, was negatively charged

-the result was a glowing beam- a cathode ray

-Thomson knew that opposites attract and he knew that the anode was probably attracting tiny negatively charged particles, which were later called electrons

-he tested this by creating a charge-to-mass ratio for electrons and found it to be constant, so electrons must be part of the atoms of all elements

Eugen Goldstein

-discovered protons as there was a positive charge opposite of the electrons in the cathode ray

James Chadwick

- discovered the neutron

Robert Millikan

-Robert A. Millikan found how much charge an electrons had, he used Thomson's charge-to-mass ratio of electrons to calculate the mass of electrons

Ernest Rutherford

-Rutherford's Gold-Foil Experiment

-wanted to test theory of atomic structure, used alpha particles in narrow beam directly at a sheet of gold

-a majority of the alpha particles passed straight through the gold atoms, with only a small fraction bouncing off the gold foil at large angles, even back to the source

-Rutherford Atomic Model

-based on the experiment, he said most of the atom is empty space, which is why barely any particles deflected

-concluded that the concentration of positive charges in a small region could have enough power for the deflection of the particles

-he called this region the nucleus

Particle	Proton	Neutron	Electron
Location	nucleus	nucleus	Energy levels outside the nucleus
Real mass	1.67 x 10^-24 g	1.67 x 10^-24 g	9.11 x 10^-28 g
Relative mass	1 amu	1 amu	0 amu
Real charge	+1.6 x 10^-19 coulombs	0 coulombs	-1.6 x 10^19 coulombs
Relative charge	+1	0	-1

-electrons are so small compared to protons and neutrons that they are basically 0 amu

Atomic number vs. Mass Number (has to be whole number)

-Atomic number- number of protons, tells you what atom you have

-unique for each element

-change the atomic number, you have a different element

-Mass number

-sum of protons and neutrons

-mass is measured in amu

-All atoms of the same element must have the same number of protons

-Not all atoms of an element have the same mass

-Isotopes, same number of protons, different number of neutrons

Elemental (isotopic) notations

-elemental symbol- in the middle

-Atomic number- on the bottom

-Mass number- on the top

-because the mass of electrons are so small, they are not counted when calculating the mass of an atom

-nuclear notation- Na-23, Na-24

-Atoms are neutral

-protons and electrons are =

-any change to the number of electrons will cause an atom to have a positive or negative charge

-ion- atom that is charged because it lost or gained electrons

-Cation- positive charge, take away electrons

-Anion- negative charge, add electrons

-the loss or gain of electrons can be represented in the isotopic notation by placing it to the upper right of the element

-Mass number= sum of proton and neutrons in an atom

-Atomic number- number of protons

-Atomic mass is the weighted average of the isotopes of an element

-Atomic mass is calculated and you need 2 things:

-the abundance in nature (%) of every types of isotope of that element

-the mass number of each isotope

-Example: Barium naturally occurs as Ba-56. But, there are over 40 isotopes of barium. Every one of them must be included in the calculation of atomic mass.

Early models of the atom- Who came up with each of these ideas?

-Solid spheres- Dalton

-Plum pudding- Thomson

-Planetary- Rutherford, atoms are mostly empty space, there is a tiny nucleus that could deflect particles

Quantum Mechanical Model (Electron Cloud Model)- cannot see an atom, it is like a fuzzy cloud

-Einstein- proposed the dual wave-particle nature of light, particles are called photons

-De Broglie- developed the wave theory of matter

-Heisenberg- stated it is impossible to know particle velocity and position at the same time

-Maxwell- discovered the photoelectric effect- when electrons hit things, they have different effects

Schrodinger's Quantum Mechanical Model

3-D model- analogous to a beehive of electrons in constant and rapid motion around a nucleus

-the electron cloud is a blur of electrons moving around the nucleus in energy levels

-electrons are found in a region of high probability called an orbital, areas where you are most likely to find electrons at any point of time

-Each electron is assigned 4 specific and unique quantum numbers, which identify an electron's energy and spin

-the principle energy level is assigned a number (1 to 7) that corresponds to the rows on the periodic table

-each row of the periodic table represents a specific principal energy level

-every principle energy level is divided into 4 sublevels

-A sublevel represents the area of probability in which that electron can be found

-the letters are s, p, d, and f

-s- sphere or a ball, 1 orbital

-levels 1-7 each have 's'

-p- 3 orbitals

-levels 2-7 each have 'p'

-d- 5 orbitals

-levels 3-6 each have 'd'

-f- 7 orbitals

-levels 4-5 each have 'f'

-all you have in principle energy levels is an s, it is closest to the nucleus so there is not much space, etc.

-Every orbital holds a maximum of 2 electrons (2e-)

-Any s can hold up to 2 electrons

-Any p can hold 6

-Any d can hold 10

-any f can hold 14

-not all sublevels are found in each energy level:

-closer to the nucleus, less sublevels found

-farther from the nucleus, more sublevels are found

Aufbau- German word which means "build up" or "construction"

-electrons fill the inner energy levels first, attracted to nucleus, but also want to get out

-first energy level, lowest energy first

-the Aufbau principle is use to determine the energy filling order of electrons

-electrons enter levels of lowest orbital energy first

-more energy is farther out

-written in energy-filling order, the electron configuration for an atom could be:

-Rutherford's atomic model could not explain the chemical properties of elements

Bohr Model of the Atom- has a set pathway of where electrons can move

-proposed that an electron is found only in specific circular paths around the nucleus

-the electron is at a set distance from, the nucleus, an orbit

-could explain how electrons could jump from ring to another only

-this model couldn't be applied to energy regions

-could not be applied to larger atoms

-A quantum of energy is the amount of energy required to move one electron from one energy level to another

-electrons are usually lost or gained from the outermost energy level of the atom, the valence shell (magic number in outer levels is 8)

-This happens so the outermost energy level of the e-configuration will be filled (more stable)

-When an atom gains or loses electrons, it is trying to become more like a noble gas

-2e- in the first energy level and 8 in the outer s and p energy levels

-Atoms and ions with the same e-configuration are called isoelectronic

-when gaining or losing electrons, take away from the outer most energy level

-orbital diagrams can be used to represent the distribution of electrons around the nucleus

-specific concepts are applied to orbital diagrams

-Pauli Exclusion Principle

-only 2 electrons can occupy an orbital and they must have opposite spins

-Hund's Rule (urinal rule)

-when electrons occupy orbitals of equal energy, one electron enters each orbital until all the orbitals contain one electron with parallel spins

-Shorthand notation (noble gas configuration)

-use a noble gas as the core and add on the outermost electrons

-noble gases are stable

Since electrons are related to energy and light is a form of energy, there is a need to look closer at light

-if electrons are given energy (from heat or electricity), then the electrons become excited and move out to a higher energy state

-Since that is not the normal position of an electron, they move back down to their original state

-Bright line spectrum- every element, when electrons move give off a pattern

-shorter the wavelength, the higher the energy

-When atoms absorb energy, electrons move into higher energy levels, and these electrons lose energy by emitting light when they return to lower energy levels

-When an electron absorbs energy, it moves out to a higher energy level- excited state

-The electron must return to its original position

-each movement releases energy in the form of light

-In its original position, the electron is in the ground state

-electrons give off energy as they move from level to level

-the bright line spectra of elements can be seen using a spectroscope

-the wavelength of light can be measured and used to calculate the energy of electrons

-every element has its own pattern so you can tell which one is which

-Wavelength (A)- uses units of length such as cm, m, and mm

-Frequency (v)- is a measure of the # of waves that pass a given point in one second

-The units of frequency are: Hz= 1/sec = sec^-1 = waves/sec

3 important equations to know

-An equation relating wavelength (A) and frequency (v) to the speed of light- c

C = Av (c = 3.00 x m/s)

-An equation relating to energy E and frequency (v)

-E = hv (h represents Planck's constant = 6.626 x J/sec

-An equation relating energy- E to wavelength- A and the speed of light- c

-E = hc/A

-only a few atoms "promote" electrons

In the d sublevel, they could be so close to the 5 or the 10, that they will pull 1 electron from the s sublevel

An example is copper (Cu)

-The number of electrons hasn't changed. Just their distribution

There were two scientists working on their own versions of how the elements at the time could be organized

-Meyer

-Mendeleev

-won the race, given credit for two reasons:

-publishing (published first, titled the Father of the Periodic Table)

-predicting elements

-his table was arranged by atomic mass

-Each (independently) found a connection between atomic mass and the physical and chemical properties of an element

-Mendeleev's table was arranged slightly do the elements are now in order of increasing atomic number

-birth of the periodic table

Types of Elements

-Metals

-elements that are generally shiny solids at room temperature

-they are good conductors of heat and electricity

-most elements are metals

-Properties of metals:

-ductility, can be drawn into wires

-malleability, can be hammered to change shape without breaking

-high luster, freshly cut surface that is caused by metal's ability to reflect light

-nonmetals

-elements that are non-conductors of heat and electricity

-most are gases at room temperature, brittle

-Metalloids

-elements with properties of both metals and nonmetals

-behavior can be controlled by changing the conditions

How can you find the number of valence electrons in an atom?

-S and p combined gives you the number of valence electrons

Are ions predictable on the PTE?

-yes, you just find out how many electrons can be lost or gained from an element to become a noble gas

-chemists used the properties of elements to sort them into groups

-In 1829, J.W. Dobereiner grouped elements into triads with similar chemical properties

There were two scientists working on their own versions of how the elements at the time could be organized

-Meyer

-Mendeleev

-won the race, given credit for two reasons:

-publishing (published first, titled the Father of the Periodic Table)

-predicting elements

-his table was arranged by increasing atomic mass

-Each (independently) found a connection between atomic mass and the physical and chemical properties of an element

-Mendeleev's table was arranged slightly do the elements are now in order of increasing atomic number

-birth of the periodic table

-In the modern periodic table, the elements within a column, or group have similar properties

-The periodic law: When elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties

-The periodic table displays the symbols and names of the elements, along with information of the structure of their atoms

-Group 1A atoms are called alkali metals

-Group 2A atoms are called alkali earth metals

-The nonmetals of Group 7A are called halogens

-elements in the "d" block are called transition metals

-elements in the "f" block are called inner transition metals

-elements 1 and 114 are nonmetals

-metalloid step is right above Ge and Sb

-noble gases have highest energy levels (s + p sublevels) filled completely to 8

-Representative elements are elements with a wide range of chemical and physical properties

-some are metals, and some are nonmetals and metalloids

-In representative elements, the highest energy levels (s + p) are not filled completely

-the number of electrons in the highest occupied energy level equals the group number

Transition Elements (d and f blocks)

-Transition metals- contain electrons in the highest occupied s level and nearby d sublevel

-colored compounds that can absorb visible light

-Inner transition metals- highest occupied s level and nearby f level contain electrons

-the shielding effect is constant for all elements in a period

-the shielding effect increases going down a group

-nuclear charge increase down a group and across a period

-Atomic radius

-one half the distance between the nuclei of two atoms of the same element when the atoms are joined

-atomic size increases from top to bottom and decreases from left to right

-Ionization Energy

-the amount of energy required to remove an electron from an atom

-decreases from top to bottom and increases from left to right

-Ionic radius

-size of the ion formed from an atom

-cations are always smaller than the original atom, anions are always larger than their original atom

-increases from top to bottom, decreases from left to right

-Electronegativity

-the attraction an atom has for electrons in a bond

-decreases from top to bottom, increases from left to right

-metals tend to lose electrons and become cations, while nonmetals tend to gain electrons and become anions

Ionic bonding occurs when oppositely charged particles (ions) attract

-Cations are attracted to anions

-form a crystal structure called a crystal lattice

-when put ions together, the energy to create this lattice is lattice energy

-energy goes out to create the crystal structure, lattice energy is exothermic

-most basic structure of the crystal lattice is the unit cell

-The valence electrons can be represented with an electron dot structure

-Metals tend to lose their electrons

-nonmetals want to gain based on number of valence electrons

-total charge of ions joined together has to be 0

Metals before nonmetals in formulas

-electronegativity tells us if an ion will bond or not

-metal +nonmetal = ionic bond, opposite charges attract

Pauling- made the electronegativity difference
1. Made a ratio from 0.0-4.0
2. Elements that have the highest electronegativity have the higher number
3. First look if elements are metals and nonmetals- THIS IS THE FIRST STEP, IF THEY ARE ONE OF BOTH, THEN IT IS IONIC
4. Find the difference between the electronegativity numbers
5. If the difference is greater than 1.7, it is ionic

CCR- Criss-Cross-Reduce

Ionic compounds can be made by the combination of any of the following ions

Metal cations with nonmetal anions

Metal cations with polyatomic anions

Polyatomic cations with nonmetal anions

Polyatomic cations with polyatomic anions

There are ionic compounds made of metal elements that have a variable charge

-ionic compounds are compounds composed of cations and anions

-Although they are composed of ions, ionic compounds are electrically neutral

-the total positive charge of the cations equals the total negative charge of the anions

-The electrostatic force that hold ions together in ionic compounds are called ionic bonds

-In ionic bonds, anions attract to cations because of opposite charge and are held together by electrostatic forces

-A chemical formula shows the kinds and numbers of atoms in the smallest representative unit of a substance

-it does not represent a discrete unit, but refers to a ratio known as a formula unit

-A formula unit is the lowest whole-number ratio of ions in an ionic compound

-NaCl has a 1:1 ratio, in a formula the formula units are the subscripts of the element and their lowest reduced ratio

Properties of Ionic Compounds

-Ionic compounds are crystalline solids at room temperature

-the large attractive forces between the cations and the anions in the compound result in a stable structure

-ionic compounds generally have high melting points

-Ionic compounds can conduct an electric current when melted or dissolved in water

-The coordination number of an ion is the number of ions of opposite charge that surround the ion in a crystal

-Polyatomic ions are cluster of ions with a charge

-The ions produced when chlorine or other halogens gain an electron are called halide ions

-The valence electrons of metal atoms can be modeled as a sea of electrons

-The valence electrons in metals are mobile and can drift freely from one part of the metal to another

-Metallic bonds consist of the attraction of the free-floating valence electrons for the positively charged metal ions

-Metals are strong conductors of electricity and heat because electrons can move freely in them

-Metals are ductile and malleable

-Metal atoms are arranged in very compact and orderly patterns

-Many closely packed arrangements are possible

3 arrangements:

-body-centered cubic (chromium, iron, sodium, potassium)- every atom has 8 neighbors

-face-centered cubic (gold, copper, silver, aluminum, lead)- every atom has 12 neighbors

-Hexagonal close-packed (zinc, magnesium)- every atom has 12

Alloys: a mixture of two or more elements, with at least one being a metal

-Alloys are important because their properties are often superior to the ones of their components

-most important alloys today are steel, have many important properties such as hardness, toughness, ductility, corrosion resistance

Substitutional alloy-If the atoms of the components in an alloy are about the same size, they can replace each other in the crystal

Interstitial alloy: If the atomic sizes of the components of the alloy are different, the smaller atoms can fit into the interstices (spaces) between the atoms

-Gilbert Lewis created the octet rule

-Metallic substances are made only of metal atoms

-these substances can be made of the pure element, such a silver or gold

-In most cases, the substance is a mixture of metals called an alloy

-Metal atoms connect to one another through metallic bonding

-This happens because of delocalized electrons and positively charged ions

-these valence electrons of metal atoms are mobile and move throughout the metal

-The idea of metals having a sea of electrons was developed by Paul Drude in the early 1900s

This gives metals certain properties:

-Malleability- the ability for metal to be hammered into shapes/sheets

-Ductility- can be pulled out into wires

-High heat capacity

-Luster- the shine on the surface of the metal

-strong conductor of heat and electricity

-Alloys are mixtures of metals (steel, tooth fillings, brass, bronze, pig iron)

-Metal mixtures can be categorized as substitutional alloys or interstitial alloys

-Substitutional

-atoms of one metal are substituted by atoms of another metal

-Interstitial

-different metal occupies interstitial spaces (holes) in the lattice structure

Roman numeral is charge on positive element that has variable charge

-if it starts with H, it is an acid

H (cl) with an element

-Hydro ----ic acid

If it is H with a polyatomic ion,

- ______ ate ---> ic, ite ---> ous acid

-Hydro is only for binary compounds

Bases have OH-

-just use normal naming (will always end in hydroxide)

Binary compound- two elements

Ternary compound- three elements

-elements have an -ide ending

-To name any binary ionic compound, place the cation name first followed by the anion name

-single element anions get ending of -ide

-To name any binary ionic compound, place the cation name first followed by the anion name

-single element anions get ending of -ide

-an acid is a compound that contains one or more hydrogen atoms and produces hydrogen ions when dissolved in water

-a base is an ionic compound that produces hydroxide ions when dissolved in water

Naming Binary Acids

-When the name of the anion ends in -ide, the acid name begins with the prefix hydro- The stem of the anion has the suffix -ic and is followed by the word acid

Naming Ternary Acids

-When the anion name ends in -ite, the acid name is the stem of the anion with the suffix -ous followed by the word acid

-When the anion name ends in -ate, the acid name is the stem of the anion with the suffix -ic followed by the word acid

Compounds can be formed from nonmetal atoms in covalent bonds

-Because the difference in electronegativity between the bonded atoms is low, the nonmetals must share valence electrons

-Duet Rule- everyone wants two electrons in the first energy level

-Octet Rule- everyone wants 8 electrons in the outer valence levels

-The covalent bond formed between nonmetal atoms in a neutral particle results in a molecule

-In a molecule, the formula is the exact type and number of atoms found in a single particle of the substance (unlike ionic compounds that are the smallest whole number ratio

-Molecule may contain atoms of the same element such as N2, O2, Cl2

-or they may contain atoms of different elements such as CO2

-Covalent bonds are classified as intramolecular forces because they exist within the molecule

-Intramolecular- bond between atoms of a molecule

-Covalent bonds can be

-single bonds (1 pair of electrons shared between two atoms)

-Double bonds (2 pairs between 2 atoms)

-Triple bonds (3 pairs of electrons between two atoms)

-Covalent bonds can be represented in LDS, structural diagram, or 3-D models

-The latter helps understand the bond geometry which plays a role in the characteristic properties of the substance

-Covalent substances tend to

-have low melting points and boiling points compared to ionic compounds or metals

-be gases, liquids or low melting point solids at room temperature

-not conduct electricity as solids or when molten

-not conduct when dissolved in water

-generally not soluble in water

A coordinated covalent bond is in which one atom freely donates both electrons to share between itself and another atom

-This is what happens in the formation of NH4+, the ammonium ion

-there are some elements whose atoms will not follow the pattern for reaching the octet

-there are suboctets and expanded octets (superoctets)

-electron deficient bonds (suboctet)

-Suboctets- atoms of elements acquires less than a full octet of eight electrons (boron)

-Superoctets- atoms of elements that expand the octet to include more than eight electrons (phosphorus and sulfur)

-For covalent bonds, bond energies and bond lengths depend on many factors:

Bond length: the distance between the nuclei of two bonded atoms

-as bond order increases, bond length decreases

Bond energies: the energy required to break one mole of the bond between two atoms

-as bond length decreases, there is more bond energy since there are more electrons being shared and there is a stronger bond

electron affinities (how much that the atom wants to hold onto their electrons), sizes of atoms involved in the bond, differences in their electronegativity, and the overall structure of the molecule

-the sum of the radii of two atoms in a covalent bond is the bond length

-Sigma bonds are formed when two atomic orbitals combine to form the molecular orbital that is symmetrical along the axis connecting the nuclei, refers to single bonds

-Pi bond form when the bonding electrons are likely to be found above and below the bond axis, they are above and below the central single bond

-Many of the properties of covalent compounds result from the three-dimensional shape and polarity of the molecules

-The shape and polarity can be determined by VSEPR (valence shell electron pair repulsion theory)

-says the outermost electrons in the valence shell in pairs repel against each other

VESPR

-The simplest molecules fall into five basic VESPR shapes

-the shapes are the result of the shared and unshared electron on the central atom

-Linear

-V-shaped (bent)

-trigonal planar

-Trigonal pyramidal

-Tetrahedal

-The other two shapes covered in your textbook are

-Trigonal bipyramidal

-Octahedral

-If there are only two atoms sharing electrons, the shape is linear (any two points makes a line)

-After that first rule, look for a central atom

-If there is a central atom, use your LDS to determine the number of atoms attached to the central atom

-The VESPR 3-D shape is based on the number of pairs of valence electrons, both shared (bonded) and unshared (unbonded)

-unshared (unbonded) pairs of electrons are also called lone pairs

-Complete the with the number of atoms attached to the central atom (if any) and the number of unshared pairs of electrons on the central atom

Shapes with a central atom	Number of atoms attached to the central atom	Number of unshared pairs of electrons on the central atom
Linear	2	0
V-shaped	2	2
Trigonal Planar	3	0
Trigonal Pyramidal	3	1
Tetrahedral	4	0
Trigonal Bipyramidal	5	0
Octahedral	6	0

Naming binary covalent compounds

-look at prefixes and suffixes

-Begin by the naming the apparently positive element with its exact name

-If there is more than one atom, use a prefix

-Next, name the apparently negative elements with its name an -ide ending

-Always use a prefix

Prefixes:

1-mono

2-di

3-tri

4 Tetra

5 Penta

6 Hexa

7 Hepta

8 Octa

9 Nona

10 deca

-If placing a prefix in front of an element creates a similar vowel sound, the vowel is usually dropped from the prefix and they are blended together

-For tri and iodide, it remains triiodide

Molecule- a neutral group of atoms joined together by covalent bonds

-a compound composed of molecules is called a molecular compound

-Molecular compounds tend to have lower melting and boiling points than ionic compounds

-Molecular compounds are usually gases or liquids at room temperature

-or low melting solids

-A compound composed of molecules is a molecular compound

-A molecular formula is the chemical formula of a molecular compound

-shows how many atoms of each element a molecule contains

-In forming covalent bonds, electron sharing usually occurs so that atoms attain the electron configurations of noble gases

-A structural formula represents the covalent bonds by dashes and shows the arrangement of covalently bonded atoms

Coordinate Covalent Bonds

-A coordinate covalent bond is a covalent bond in which one atom contributes both bonding electrons

-In a structural formula, you can show coordinate covalent bonds as arrows that point from the atom donating the pair of electrons to the atom receiving them

-In a coordinate covalent bond, the shared electron pair comes from one of the bonding atoms

Bond Dissociation Energies

-The energy required to break the bond between two covalently bonded atoms is called bond dissociation energy

-This is usually expressed as the energy needed to break one mole of bonds, or 6.02 x 10^23 bonds

-A large bond dissociation energy corresponds to a strong covalent bond

Resonance

-For example, ozone has 2 possible electron dot structures that can be converted by shifting electron pairs without moving the oxygen atoms

-Chemists believed that electron pairs would rapidly flip back and forth, or resonate

-However, the two bonds in ozone are the same length, so the electron pairs do not resonate back and forth

-The actual bonding of oxygen atoms in ozone is hybrid, or mixture, of the extremes represented by the resonance forms

-The two electron dot structures for ozone are examples of what are referred to resonance structures

-A resonance structure is a structure that occurs when it is possible to draw two or more valid electron dot structures that have the same number of electron pairs for a molecule or ion

-Although no back and forth changes occur, double-headed arrows are used to connect resonance structures

Exceptions to the Octet Rule

-The octet rule cannot be satisfied in molecules whose total number of valence electrons is an odd number

-There are also molecules in which an atom has fewer, or more, than a complete octet of valence electrons (suboctet or superoctet)

Molecular Orbitals

-When two atoms combine, this model assumes that their atomic orbitals overlap to produce molecular orbitals, or orbitals that apply to the entire molecule

-Just as an atomic orbital belongs to a particular atom, a molecular orbital belongs to a molecule as a whole

-A molecular orbital that can be occupied by two electrons of a covalent bond is called a bonding orbital

VESPR Theory

-In a tetrahedral molecule, the angles are 109.5 degrees, which is the tetrahedral angle

-According to VESPR theory, the repulsion between electron pairs causes molecular shapes to adjust so that the valence-electron pairs stay as far apart as possible

Hybrid Orbitals

-Orbital hybridization provides information about both molecular bonding and molecular shape

-In hybridization, several atomic orbitals mix to form the same total number of equivalent hybrid orbitals

Hybridization for Single Bonds

-The one 2s orbital and three 2p orbitals of a carbon combine to become 4 sp3 orbitals

Double Bonds

-sp2 hybrid orbitals form from the combination of one 2s and two 2p atomic orbitals of carbon

Triple Bonds

-a 2s atomic orbital of carbon mixes with only one of the three 2p atomic orbitals

-The result is two sp hybrid orbitals for each carbon

Bond Polarity

-When the atoms in the bond pull equally, the bonding electrons are shared equally, and the bond is a nonpolar covalent bond

-A polar covalent bond is a covalent bond between atoms in which the electrons are shared unequally

-The more electronegative atom attracts electrons more strongly and gains a slightly negative charge

-The less electronegative atom has a slightly positive charge

Polar Molecules

-In a polar molecule, one end of the molecule is negative while the other end is slightly positive

-the partial charges on the atoms in a molecule are electrically charged regions or poles

-A molecule that has two poles is called a dipolar molecule, or dipole

Types of Intermolecular Attractions

Van der Waals Forces

-Dipole interactions

-polar molecules are attracted to one another

-the oppositely charged regions of polar molecules are attracted to one another, much weaker than ionic bonds

-Dispersion (London) Forces

-weakest of all, occurs between non-polar molecules

-caused by the motion of electrons

-When the moving electrons happen to be more on the side of a molecule closest to a neighboring molecule, their electric force influences the neighboring molecule's electrons to be momentarily more on the opposite side

-Hydrogen bonds

-attractive forces in which a hydrogen covalently bonded to a very electronegative atom is also weakly bonded to an unshared electron pair of another electronegative atom (oxygen, nitrogen, of fluorine)

-There are a few solids that consist of molecules that do not melt until the temperature reaches 1000 Celsius of higher

-Most are network solids, solids in which all of the atoms are covalently bonded (example are diamonds)

-Melting network solids requires breaking down all the covalent bonds throughout the solid

-Accuracy is a term used to describe how close a measured value is to a known or accepted value (how close are you to the real value)

-For example, if students measure the mass of a crystal sample as 23.66 g, but the actual mass is only 14.23 g, then the measurement is NOT accurate because the measurement is not close to the accepted value

-A term that is often confused with accuracy is precision

-Precision refers to how similar recorded measurements are to each other

-For example, if the same students in a lab take turns using the same balance to find the mass of the same crystal substance mentioned above and they all get results around 14 grams, then the measurements are precise

-Precision is independent of accuracy

-The best situation would be having data that is both precise and accurate

How do we determine how accurate we are?

-one way to compare the experimental and accepted (true) values is by percent error

-The formula for percent error is:

Percent Error = |(acceptable (true) value - experimental value) | / acceptable (true) value x 100

-If your error is larger than 15%, you are not very accurate

-Percent yield is a measure of how close you are to the true value

-subtract the percent error from 100

-Measurements must reflect the type of tools used and the limits of those tools

Identifying Significant Figures

-What you can actually measure AND one more place that you can reasonably estimate

-It is important to understand that you cannot estimate on top of an estimate

-What numbers are significant when you record data?

-All values 1-9 in a measured quantity ARE significant.

-What about zero?

Sandwich Rule: Zero is significant when between sig figs 1-9.

-Zero is significant when marked by a decimal or a bar line.

-You will never put a bar line over a number 1-9

-Zero is significant on the right side of a measured value as long as there is a decimal point anywhere in the number

-The decimal point must belong there for a reason

-This is the Atlantic rule

-Zero is NOT significant on the left side of a measured value (even if there is a decimal point)

-In this case, zero is only a place holder; it disappears when converting to scientific notation

-This is the Pacific Rule

-Accepted values and agreed-upon ratios have an infinite number of significant figures

-Example: 1 mile = 5280 ft 4 qtrs. = 1 gal

-Exact numbers (counting numbers) have an infinite number of significant figures.

-Exact numbers are counting numbers followed by object counted.

-These are NOT measured! (25 pencils, 800 people)

RULE: When multiplying and dividing, the answer can only have as many significant figures as the least number of significant figures in the values used.

RULE: When adding or subtracting, the answer can have as many decimal places as the least number of decimals places in the values used.

Because most of our measurements use decimal places, it is easier to follow this rule when adding and subtracting

-If the values are in scientific notation, make sure to convert them to the same power of ten before adding or subtracting

-The metric system was first developed in the late 1700's in France (called SI system)

-The SI system is preferred in science because it counts in tens (or multiples of ten)

-Metrics has two major divisions of units

-Five most common SI units:

-Temperature- Kelvin

-Distance- meters

-Mass- kilograms

-Time- seconds

-Amount of substance- moles

-Base (fundamental) units- those that can be measured directly using a single tool

-Another way of looking at base units is that they have a foundation in an object or event in the physical world

-Seven quantities that have a base unit:

-Temperature- Kelvin

-Distance- meters

-Mass- kilograms

-Time- seconds

-Amount of substance- moles

-Electric current- amperes (amp)

-Luminous intensity- candelas

-Derived units- When base units are mathematically combined, a derived unit is formed

-Examples:

-Area- distance x distance = distance^2

-Volume- distance x distance x distance = distance^3 Note: 1 cm^3 = 1 mL

-Speed= distance/time

-Density= mass/volume

Kelvin = Celsius + 273

Degrees Celsius = K - 273

-Celsius is used in the everyday metric system

-Kelvin is used in the physical sciences

-Freezing point: 273.15

-Boiling point: 373.15

Error = experimental value - accepted value

Joules: SI unit for energy

Calories: the quantity of heat it takes to heat up 1 g of pure water by 1 degree

Celsius

Temperature: Celsius, Kelvins

Distance: meters, kilometers, millimeters, centimeter

Mass: grams, kilograms, milligrams

Volume: liters, milliliters, cubic centimeters

Energy: joules and calories

-1 joule = 0.2390 cal

-1 cal = 4.184 J

-A conversion factor is a ratio of equivalent measurements

-When a measurement is multiplied by a conversion factor, the numerical value is generally changed, but the actual size of the quantity measured remains the same

-Density is an intensive property that depends only on the composition of a substance, not on the size of the sample.

-The density of a substance generally decreases as temperature increases because volume increases as temperature increases but the mass stays the same

-Water is an exception to this rule

-Over a certain range of temperatures, the volume of water increases as temperatures decrease because ice, floats because it is less dense than liquid water