AP CHEM UNIT 1

element

a substance that cannot be broken down into other substances by chemical means (only one atom)

Compound

elements bonded together

what happen when the ratio of mass or atom changes?

the chemical formula changes

all pure substances are ....

element or compounds

Mixture

varying compositions; made up of a number of pure substances and either homogenous or heterogenous

What is percentage by mass composition?

the percent one element is in comparison to the entire mass of the compound. (ie mass of 2 hydrogen/ 1 H2O

How to find percentage by mass composition?

find mass of element then divide by total mass of the compound. Multiply by 100 to get percentage

What is the empirical formula?

the simplest whole number ration of the atoms in each element in that compound

What is something to be careful about with empirical formulae?

different compounds, with different molecular formulae) may have the same empirical formula

How to find empirical formula?

1) Percentage composition by mass

2)atomic mass

3) divide by atomic mass

4)divide by smallest factor

5)multiply if no whole numbers

molecular formula?

formula that tells exactly how many atoms of each element is present in a compound as opposed to the simplest whole number ration

mol

the amount of any substance that contains the same number of particles. essentially a standard number of particles

mass of an amu? What is it?

1.66e-24. the mass of an indv atom

Relative atomic mass?

the weighted average of the masses of all the atoms in a normal isotopic sample

What is an isotope?

atoms that have the same number of protons and electrons, but they have different amounts of nuetrons

How to calculate average atomic mass

multiply the weights of each isotope by its abundance and then multiply that by the other isotopes time abundance. Then divide by the the percents added up (if percent = 100 divide by 100, if not divide by that sum)

Mass spectrometry?

detect isotopes and provide evidence for their existence. Analyzing data produced from this leads to identifying isotopes and then average atomic masses (hint to identifying, is that the weighted mass will be closer to the mass that is more abundant)

How to use percent composition by mass to determine impurities?

essentially, calculate what the percentage of each element should be in a pure substance and then compare with the impure substance

Particle?

could mean atom (covalent), ions (ionic), formula units (ionic) or molecules (covalent)

What is the Rutherford atomic model based around?

a dense nucleus is surrounded by the electrons, based around the attraction b/2 the opposite protons and electrons; governed by Coulomb's law.

How did Bohr change Rutherford's atomic model?

he suggested that the electrons could only travel in fixed orbitals

How was it found that each element emitted a unique radiation pattern?

spectroscopes led to the discovery of electromagnetic radiation which emitted quanta when heated.

-radiation release was caused by e- in atom absorbing the energy and bumped to a shell further from the nucleus.

-as the electron gains and loses energy as it goes from orbital to orbital is leaves lines to create a spectrum

What happens when an electron gains a significant amount of energy?

it may eject itself from the atom entirely (ionization energy)

what was discovered about particles and fixed orbitals?

-this did not explain properties of the atom of electrons that were observed

-some scientists suggested that electrons had some wave-like characteristics

Electromagnetic radiation

considered as waves that have properties of wavelength λ and frequency nu ν

what is wavelength?

the distance between two repeating points on a sine wave?

what is frequency?

the number of waves that pass a fixed point in a second (s^-1 or Hertz)

What is the equation to relate speed of light, frequency, and wavelength?

c = λν, c is the speed of light

How to calculate the energy of a photon?

E= hν, h is plank's constant 6.626 x 10^-34 Js

What led to the quantum mechanical model of the atom we know today?

-schroedinger wave theory

-Heisenberg uncertainty principle

What is wave theory?

solved wave equations to make predictions about where an electron would likely be found in an atom

what is the uncertainty principle?

you cannot devise an experiment that tells you both the position and momentum of an electron)

What is the current model of the atom?

3d maps where any electrons could be found at any time within the shells

What is an oribital?

3d probability maps predicted by Schrondinger which describe the likely positions of electrons within the atom

how to get max number of electrons in each shell

2n^2; n is the shell number

What are shells divided into?

subshells

how to know how many subshells are in a shell?

it is proportional to the shell number (ie shell 1 has one sub shell, shell 2 has 2 subshells and so on)

How many orbitals in each subshell s,p,d,f?

1, 3, 5,7 respectively

how many electrons can each orbital hold?

2, so an s and 4, p 6, 5 10, 7 14

What is Pauli's exclusion principle?

-all electrons in a single atom must be unique so if electrons are in the same orbital as another, they distinguish themselves via spin

Aufbau process (rules for filling orbitals)

1) electrons present

2)lowest energy orbitals are filled first (1s, 2s, 2p etc.)

3)Hund's rule of multiplicity

what is the trouble with 4s and 3d?

consider 4s as having a slightly lower energy than 3d and assume the 4s is filled before the 3d

what is hund's rule of simplicity?

if there is more than one orbital with the same energy, one electron is placed into each orbital before any pairing will take place.

Noble gas core Electronic config?

place the nearest noble gas in brackets then continue with the EC

ions and electronic config?

write electronic config and then change with the ion. Keep in mind that d blocks will lose the 4s electrons first

What is the photoelectric effect?

by using high-energy UV or Xray photons, electrons can absorb enough energy to be ejected from the atoms.

What is PES used for?

gather data abt the e- structure of an atom

What energy do the photons used to eject electrons have?

E = hν

How are Ionization energy and photon energy related?

the photon energy is greater than that of the ionization energy

ionization energy in a table?

the large jump indicates the attempt to remove an electron from a core state

When can you determine the second ionization energy?

you can only find the second, once you remove the first electron

how are PES and IE different?

PES knocks out an electron from a new atom everytime. IE continues to knock out electrons from the same element

paramagnetic?

attracted by a magnet, unpaired electrons

diamagnetic

slightly repelled by magnets, all electrons paired

isoelectric

isoelectronic series have the same EC as other things, so another identifying factor like protons should be given

The chemical and physical properties of elements and compounds are dependent at what?

valence electrons configurations

What leads to periodic law/periodicity

a regular change in protons and therefore a regular change in the outermost electronic config and therefore repeatable patterns can be observed

Properties of noble gasses?

all of the s and p orbitals are filled so they need a lot of energy to remove electrons. As a results, they are very unreactive and don't tend to form compounds

Alkali metal and alkaline earth (g1 and 2)

Group 1 are nobled gasses plus one electrons and then tend to form 1+ since they want to be noble gasses

-group two tends to form 2+ since they are two above a noble gas (same with 13)

group 16 and 17 non-metals?

EC of [noble gas] s^2p^4 which mean they'll gain two p electrons to form a noble gas. hence the 2- charge

17- EC of [noble gas] s^2p^5 means it will gain one electron resulting in a 1- charge

first Ionization energy?

the energy required to remove one mol of electrons from one mole of gaseous atoms to produce one mole of gaseous ions (measured in KJ mol-1 (positive since energy must be put in aka endothermic)

How to determine magnitude of ionization energy?

nuclear charge (the number of protons)

-distance from the nucleus

What will happen to ionization energy from left to right in a period?

it will steadily increase because there is more proton charge but from the same distance

What happens to ionization as you go down a group?

it decreases because the electrons get further from the nucleus and therefore the Coulumbic is less

Is nuclear charge or distance more important?

distance

Why do boron and aluminum have a lower ionization energy?

Elements in group 13 have an EC of s^2p^1c. Since the outer p^1 is in the p orbital which has slightly higher energy than the s orbital and further away than the nucleus. Hence, since the distance is slightly larger, the IE should be lower than you expected

Why do Oxygen and Sulfur have lower IE than expected?

group 16 have EC of s^2p^4. The electron that is removed in the ionization process is paired in a p orbital so it experiences repulsion. Due to this repulsion, the electron is easier to lose, so the IE is lower than expected

Why is it harder to remove a second electron from an atom?

there is a reduced mutual repulsion and the electrons move slightly closer to the nucleus and by coulombs law, the coulombic attraction is stronger. Also the electrons are being removed from a positive ion

How does atomic size change across a period?

it decreases from left to right since the nuclear charge increases, the electrons are in the same shell -> higher coulombic attraction

How does Atomic size differ up and down a group?

the size increases b/c although the nuclear charge increases, the valence e- are further from the nucleus. The size increases because there are more shells occupied

Size of Cations?

the remaining electrons experiences less repulsion and is drawn in closer than the atom, therfore the radius is smaller than that of the atoms.

-also, an atom loses all the valence electrons which decreases size compared to the parent

Size of anions?

when gaining electrons, the extra electrons tend to repel causing the anion to be larger than the parent

Electron affinity?

the energy change when one mol of electrons is added tto one mol of gaseous atoms, to produce one mole of gaseous ions

-exothermic and energy is released

how does electrical affinity change down a group?

less negative down a group since the electrons are added to shells that are further from the nucleus and then less coulombic atraction

Why is second electrical affinity so much harder?

using oxygen as an example, the affinity is positive and endothermic since the second electron must be forced into an already negative species

Electronegativity

the ability of an atom within a covalent bond to attract electrons to itself.

How to tell which element is most electronegative?

the halogens and fluorine is most electronegative. non-metals want to gain electrons to be stable and metals tend to lose electrons to get filled subshells so non-metals have higher electronegativities and metals are less electronegative

How does electronegativity change down a group? a period?

decrease down a group. Increase across a period

how do physical properties change within a group?

-tend to change uniformly

-there are gradual changes

Physical properties across a period?

harder to predict, BUT sometimes values of a property may peak and then reverse

Chemical properties within a group?

-as the ionization energy decrease, the reactivity increases

-it also makes sense that group one atoms are more reactive since they only need to lose one electron instead of two.

Chemical properties across a period?

metal elements on the left form basic oxides.

-oxides of non-metals are acidic

-change occurs at group 13 which acts amphoterically.

If something doesn't react with water how to determine if a base or acid?

if it is a base, it will react with an acid and if it is an acid, it will react with a base