CHEM2070 Prelim 1 content

measurement

a comparison of a quantity to a standard unit, the number by itself is not enough; the unit gives meaning

SI units

the internationally accepted system for science based on standardized base units

derived units

the units formed by combining SI base units through mathematical relationships such as multiplication or division

taking measurements

not all measurements are equal, depend on precision and accuracy

what are significant figures?

Significant figures are the digits in a measurement known with certainty, plus one estimated digit. Indicate the precision of a measurement

what is accuracy?

accuracy is how close a measured value is to the true or accepted value

what is precision?

how close repeated measurements are to each other

what is the mole?

mole (mol) is the SI unit for amount of substance. 1 mole = 6.022 × 10²³ particles (AKA Avogadro’s number)

Addition and subtraction sig fig rules

round the answer to the same decimal place as the least precise measurement

multiplication and division sig fig rules

round the answer to the same number of significant figures as the measurement with the fewest significant figures

dimensional analysis

a method for converting one unit into another—treats units like algebraic quantities (units should cancel)

conversion factors

A ratio = 1, changes the unit without changing the quantity, if it’s known exactly it has infinite sig figs

factor-label method

start with the quantity you know, multiply by conversion factors so units cancel, only keep the target unit in final answer

converting between different quantities

requires using physical relationships (density, specific heat, etc *measured so limited sig figs)

using multiple units (dimensional analysis)

A rate contains more than one unit (mph), so each unit may need its own conversion factor

empirical observations of matter

see matter in many phases (solids, liquids, gas), see that matter can separate or combine

solids

definite shape and volume

liquids

definite volume, takes shape of container

gases

no definite shape or volume

categorizing matter

use chemical and physical properties

physical properties

what is it like? (state of matter, color, density, physical changes)

physical changes

changes to a physical property

chemical changes

changes to a chemical property

chemical properties

how can we transform it (flammability, electrochemical reactivity, interaction with other substances)

flammability

can we set it on fire?

electrochemical reactivity

can we electrolyze it (use electrical energy to cause a chemical reaction, usually by breaking a compound into simpler substances)

intensive properties

do not depend on the amount of matter (density, color, boiling point, temperature, reactivity)

extensive properties

depend on the amount of matter (mass, volume, energy released upon combustion)

the atomic perspective

A central concept in the central science—the state of matter depends on the arrangement and motion of extremely tiny particles (what drives transformation in matter is the particles’ energy)

elements

a pure substance made of only one type of atom that cannot be broken down into simpler substances by chemical means

what is the island of stability

a predicted region of the periodic table containing superheavy nuclei that may be relatively more stable and have longer half-lives than nearby superheavy elements

what happens when elements combine

elements can combine in specific ratios to form compounds, creating substance with properties different from the original elements

classifying substances

identifying substances based on their composition and determining whether it is an element, compound, or mixture

compound

a pure substance made of two or more different elements chemically bonded together in a fixed ratio

pure substance

matter with a constant, uniform composition and consistent properties. can be an element or a compound

mixture

a combination of two or more substances that are physically combined, not chemically bonded. the substances retain their individual properties and can generally be separated by physical methods

homogenous mixture

A mixture with a uniform composition throughout. its components are evenly distributed (ex: salt water)

heterogenous mixture

a mixture with a non-uniform composition in which different parts can have different properties or compositions (ex: oil and water)

kinetic energy

the energy an object or a particle has because of its motion

temperature

a measure of the average kinetic energy of the particles in a substance. higher temperature means particles have greater average kinetic energy

potential energy

stored energy that an object or system has because of its position, arrangement, or interactions.

how can energy be transferred?

energy can be transferred between a system and its surroundings primarily through work or heat

what is work as a way of transferring energy

the transfer of energy that occurs when a force causes an object to move. W = Fd (F=force, d=distance moved in direction of the force)

what is heat as a way of transferring energy?

Heat (q) is the transfer of thermal energy between objects or systems due to a temperature difference. energy flows from the hotter object to the colder object

atom

the smallest unit of an element that retains the chemical properties of that element

basic structure of an atom

an atom has a small, dense nucleus containing protons and neutrons, surrounding by a fuzzy cloud of electrons

proton

a positively charged (+1) subatomic particle found in the nucleus. its mass is approximately 1 amu

neutron

a neutral subatomic particle found in the nucleus. its mass is approximately 1 amu (about the same as a proton)

electron

a negatively charged (-1) subatomic particle found in the electron cloud. its mass is approximately 5.5 × 10^-4amu (much smaller than proton or neutron)

Rutherford gold foil experiment

Fired alpha particles at a thin sheet of gold foil—most passed straight through, but a small number were strongly deflected. concluded that atoms are mostly empty space with a small, dense, positively charged nucleus

nucleus of an atom

The tight, compact center of an atom containing protons and neutrons. contains almost all of an atom’s mass

atomic symbol

a shorthand notation that identifies an element and can show its atomic number and mass number

atomic number

the number of protons in an atom’s nucleus. it identifies the element.

mass number (total weight)

total number of protons + neutrons in an atom

atomic mass (atomic weight)

the weighted average mass of all naturally occurring isotopes of an element, measured in atomic mass units (amu)

isotope

atoms of the same element that have the same number of protons but different numbers of neutrons

difference between mass number and atomic mass

mass number = protons + neutrons in one specific atom/isotope. atomic mass = weighted average of the masses of all naturally occurring isotopes of the element

periodic table

table that organizes elements by increasing atomic number and groups elements with similar chemical properties together

groups of the periodic table

the vertical columns of the periodic table. elements in the same group generally have similar chemical properties and similar number of valence electrons

periods on the periodic table

the horizontal rows of the periodic table. elements of the same period have the same number of occupied electron shells/energy levels

what determines the identity of an element

number of protons in its nucleus (changing the number of protons changes the element)

group 1 - Alkali metals

(Li, Na, K, Rb, Cs, Fr) very reactive metals, have 1 valence electron, commonly form +1 ions, and become more reactive down the group. Generally soft and have relatively low melting points

group 2 - Alkaline Earth Metals

(Be, Mg, Ca, Sr, Ba, Ra) reactive metals, have 2 valence electrons, commonly form +2 ions, and generally become more reactive down the group

group 16 - chalcogens

(O, S, Se, Te, Po, Lv) have 6 valence electrons and tend to gain or share electrons to achieve full valence shell. oxygen and sulfur are particularly common nonmetals (but group includes metalloids too)

group 17 - halogens

(F, Cl, Br, I, At, Ts) Highly reactive nonmetals, have 7 valence electrons and commonly gain 1 electron to form -1 ions. reactivity generally decreases down the group

group 18 - noble gases

(He, Ne, Ar, Kr, Xe, Rn, Og) very unreactive gases (full valence electron shells) colorless and exist as individual atoms rather than molecules under ordinary conditions

metals

generally shiny, malleable, ductile, and good conductors of head and electricity. tend to lose electrons and form cations (positive ions). located primarily on the left and center of the periodic table

nonmetals

generally poor conductors, and many are brittle has solids. tend to gain or share electrons. located primarily on the upper right of the periodic table (plus hydrogen)

metalloids

have properties between those of metals and nonmetals. Many are semiconductors. found along the stair step line separating metals and nonmetals (common metalloids: B, Si, Ge, As, Sb, Te)

ionic compounds

substances made of positive and negative ions held together by electrostatic attraction. typically form when a metal transfers electrons to a nonmetal (ex: NaCl)

molecules

two or more atoms covalently bonded together and acting as a discrete unit (ex: H₂O)

covalent bond

a chemical bond formed when two atoms share electrons. usually occur between nonmetal atoms

molecular formula

shows the actual number of each type of atom in one molecule (ex: C₆H₁₂O₆ has 6 carbon, 12 hydrogen, 6 oxygen atoms)

empirical formula

shows the simplest whole-number ratio of atoms in a compound (molecular formula C₆H₁₂O₆ has the empirical formula CH₂O)

difference between molecular formula and an empirical formula

molecular formula gives the actual number of atoms in a molecule, empirical formula gives the simplest whole number ratio of those atoms

what are the different ways to represent molecules

Molecules can be represented using structural formulas, perspective drawings, ball-and-stick models, and space-filling models. Each representation emphasizes different information about the molecule.

what is a structural formula

A drawing that shows which atoms are connected and how they are bonded. Lines represent covalent bonds.

what is a perspective drawing of a molecule

a drawing that represents the three-dimensional arrangement of atoms using different types of bonds to show atoms projecting toward or away from the viewer.

ball and stick model

A 3D model in which balls represent atoms and sticks represent bonds. It emphasizes the molecule's shape and bond angles.

space filling model

A model in which atoms are represented by overlapping spheres sized according to their relative atomic sizes. It shows the molecule's overall shape and how much space the atoms occupy.

ionic compound

a compound made of cations and anions held together by electrostatic attraction (usually between metals and nonmetals)

ion

an atom or group of atoms that has a net electrical charge because it has gained or lost electrons

cation

positively charged ion formed when an atom loses electrons

anion

a negatively charged ion formed when an atom gains electrons

single atom ions (monatomic ions)

ions consisting of one atom that has gained or lost electrons (like those in group 1, group 2, group 16, and group 17)

polyatomic ions

ions made of two or more covalently bonded atoms that carry an overall charge

how are ionic compounds named

cation is named first, followed by anion (ex: sodium chloride)

fixed charge cation

metal ion forms one predictable charge (groups 1 and 2 are common examples)

variable charge cation

a metal that can form more than one possible charge (commonly transition metals) charge is indicated using a roman numeral in the compound’s name (ex: FeCl₂ → iron (II) chloride

how are monatomic anions named in ionic compounds

change the ending of the element’s name to -ide

what are molecular (covalent) compounds

generally made of nonmetal + nonmetal atoms connected by covalent bonds

how is the first element in a molecular compound named

use the full name of the element (use a numerical prefix if there is more than one atom of that element)

how is the second element in a molecular compound named

use a numerical prefix to indicate the number of atoms and change the element’s ending to -ide

what prefixes are used when naming molecular compounds

mono-,di-,tri-,tetra-,penta-,hexa-,hepta-,octa-,nona-,deca-

acids

substances that produce H⁺ ions (or H₃O⁺ in water) when dissolved in water

binary acids

an acid containing hydrogen and one other element, with no oxygen (ex: HCl (aq) → hydrochloric acid

oxyacid

name depends on the ending of the polyatomic ion (-ate→-ic acid, -ite→ -ous acid)

alkanes

organic compounds containing only carbon and hydrogen with single bonds between carbon atoms. saturated hydrocarbons (simplest organic molecules)

parent chain of an alkane

the longest continuous chain of carbon atoms in the molecule—its length determines the base name

suffix for alkane

-ane (ex: methane, ethane, propane)