unit 1: atomic structure and properties

avogadro's number

avogadro's number

6.022 x 10^23 atoms/mol

atomic mass unit (amu)

a unit of mass equal to one-twelfth the mass of a carbon-12 atom (measures the weight of atoms--NOT THE SAME AS MOLAR MASS)

columns on the periodic table

called groups, 18 total, eg. halogens, noble gases, etc

rows on the periodic table

called periods, go left to right, 7 in total

atomic number

the number of protons in the element; defines the element and its properties

atomic mass

average mass of all the isotopes of an element--basically the mass of 1 atom of that element

molar mass

weight of 1 mole of a substance (in grams). found by adding up the atomic masses of each element in a compound. can also be the atomic mass if there is just 1 element

molarity

moles of solute/liters of solution

isotopes

atoms of the same element with different numbers of neutrons

mass spectrometry

a technique used to measure the mass of components in a sample. it is usually a graph with the % abundance of each isotope of an element

average atomic mass

the weighted average (% abundance x atomic mass for each isotope) added together and divided by the number of isotopes

mass number

the sum of the number of neutrons and protons in an atom

pure substance

matter that has uniform properties and compostion throughout

elemental substance

substance made of a single element

compound

substance made from more than 1 element

molecule

2+ atoms held together by a chemical bond (can be a covalent or ionic compound)

formula unit

lowest whole number ratio of ions (used for ionic compounds--basically the empirical formula)

naming ionic compounds

• don't use prefixes

• positive ions (cations) come first, negative ions (anions) come second

• NH4+ = ammonium; start with this if it is present

• monatomic anion: replace ending to -ide (ex FeO = iron(II) oxide)

empirical formula

a chemical formula with the lowest whole number ratio of each atom. can be the same as the molecular formula

molecular formula

a chemical formula showing the actual number of each type of atom in a molecule

• find empirical formula, then divide molecular formula mass by empirical formula mass

• multiply the subscript of each element (the small number) by the resulting number from the above division

percent compostion/mass percent

percent (by mass) that an element contributes to the total mass of a compound

law of definite proportions

a given pure compound is always made of the same elements in the same proportions

homogenous mixture

uniform texture throughout

heterogeous mixture

mixture where different substances can be distinguished from the rest of the mixture

coloumb's law

states that like charges repel and opposite charges attract, with a force proportional to the product of the charges and inversely proportional to the square of the distance between them

quantized electrons

electrons cannot exist between levels, only in whole-number levels

high electron shell energy

farther from nucleus, unstable, more likely to change (more likely for electrons to jump)

low electron shell energy

closer to nucleus, more stable, less likely to change, harder to remove through ionization (high ionization energy)

core electrons

non-valence electrons

ionization energy

energy required to remove an electron from an atom, usually the outermost subshell. increases right across the periodic table, decreases down the periodic table. fewer protons relative to electrons (+ larger atomic radius) = lower ionization energy because electrons can be more easily pulled off

afbau principle

electrons fill lowest energy subshells first

pauli exclusion principle

electrons in the same orbital must have opposite spins

hund's rule

electrons fill orbitals singly before pairing up

photoelectron spectroscopy (pes)

graphs showing how much energy is required to remove electrons from an atom completely. peaks show the numbers of electrons in specific subshells

electron shielding

core electrons shield valence electrons from full charge and pull of the nucleus. increases down the periodic table

atomic radius

distance from the nucleus to the outermost electron in a neutral atom. decreases across the periodic table (since more protons increase pull on electrons), increases down the periodic table

ionic radius

distance from the nucleus to outermost electrons in an ion. cations have smaller radii, anions have larger.

electron affinity

the energy difference that results when an electron is added to an atom (halogens have high electron affinities). it is a positive number when energy is released. metals are usually endothermic because they like to lose electrons, and nonmetals are usually exothermic because they like to gain electrons

electronegativity

a measure of an atom's ability to attract shared electrons that make up a chemical bond. smaller atoms usually have higher electronegativity because they are physically closer to the shared electrons, and electrons closer to filling their shell usually have higher electronegativity. decreases down the periodic table, increases right across table

effective nuclear charge

the amount of positive charge experience by each individual electron - the pull the nucleus exerts on it. electrons in outer subshells experience less effective nuclear charge. increases right across the table (nuclei have more protons), decreases down (more electrons and outer shells)