MCAT General Chemistry - COMPLETE

Nucleus

centre of atom, holds most mass, protons and neutrons

fundamental unit of charge (e)

magnitude of charge of a proton or electron (e = 1.6 × 10^-19 C)

atomic mass unit (amu)

mass of one proton or neutron, exactly 1/12 the mass of carbon-12

Proton

subatomic particle with charge of +1 e, mass = 1 amu, found in the nucleus

atomic number (Z)

identifies element, number of protons in one atom

neutron

subatomic particle with no charge of , mass > 1 amu, found in the nucleus

mass number (A)

sum of the protons and neutrons in one atom

Isotopes

Atoms that have the same atomic number but different mass numbers; have the same number of protons but varying numbers of neutrons; referred to by the name of element followed by mass number; same atomic number means similar chemical properties

Electrons

subatomic particle with charge of - 1 e, mass = 1/2000 amu (often considered 0), found outside the nucleus

Electron shell

a given distance from the nucleus, corresponding to a particular level of electrical potential energy

Valence electrons

Electrons furthest from the nucleus; strongest interactions from surrounding environment and weakest with nucleus; involved with bonding

Ion

charged atom

Cation

positively charged ion

Anion

negatively charged ion

Hydrogen Isotope Names

protium : Z=1, A=1

deuterium : Z=1, A=2

tritium : Z=1, A=3

Atomic weight

weighted average of naturally-occurring isotopes of an element; represents mass of ‘average’ atom in amu and mass of one mol of element in g.

Mole (mol)

number of things equal to Avogadro’s number

Avogadro’s number (N_A)

6.02 × 10²³

Ernest Futherford

1910 - proved atom has small, dense, positively charged nucleus - gold foil experiment

Max Planck

1899 - first quantum theory, energy emitted as electromagnetic radiation comes in discrete bundles/quanta - blackbody experiments/ultraviolet catastrophe

Quantum (pl. quanta)

discrete amount of energy

Planck relation

relates the energy of a quantum to frequency via a proportionality constant; E=hf=hν=hc/λ

Planck’s constant (h)

proportionality constant, 6.626 × 10⁻³⁴ J · s

frequency (f/ν)

wave frequency of radiation

Niels Bohr

1913 - developed planetary model of atom; quantized angular momentum

angular momentum (L)

a vector quantity that describes the rotary inertia of an object or system; L=mvr=nh/2π

Rydberg equation

E= - R_H/n²= R_H[1/n_i²-1/n_f²]; negative = attractive force towards nucleus; energy of electron increases at increasing n

Rydberg unit of energy

2.18 × 10⁻¹⁸ J/electron

orbit

defined pathway of an electron at a discrete energy level

ground state

state of lowest energy; all electrons are in lowest possible orbitals

excited state

at least one electron is at a higher energy level

Atomic Emission Spectrum

spectrum of frequencies of electromagnetic radiation emitted due to electrons making a transition from a high energy state to a lower energy state; each element has unique set of energy levels

line spectrum

representation of atomic emission spectra, where each line represents light at a specific frequency

Lyman series

hydrogen emission lines from n ≥ 2 to n = 1

Balmer series

hydrogen emission lines from n ≥ 3 to n = 2

Paschen series

hydrogen emission lines from n ≥ 4 to n = 3

Atomic Absorption Spectrum

the fraction of incident radiation absorbed by the material over a range of frequencies of electromagnetic radiation; electrons absorb specific amounts of energy to get excited; equal to emission wavelengths

orbitals

regions of space where electrons are often localised, holds two electrons of opposite spins

Heisenberg Uncertainty Principle

It is impossible to simultaneously determine, with perfect accuracy, the momentum and the position of an electron.

Quantum numbers

numbers that describe electrons in an atome

Pauli Exclusion Principle

No two electrons in a given atom can possess the same set of four quantum numbers.

Principal quantum number (n)

represents energy level/electron shell, any positive integer value, max # electrons in shell - 2n²

azimuthal (angular momentum) quantum number (l)

shape and number of subshells within given shell; integers btwn 0 and n-1, max # electrons in subshell = 4l+2

Spectroscopic notation

shorthand representation of the principal and azimuthal quantum numbers; l=0=s, l=1=p, l=2=d, l=3=f

magnetic quantum number (m_l)

specifies orbital; integers from -l to l, including 0; 2 electrons per orbital

spin quantum number (m_s)

specifies spin orientation, ±½

paired electrons

two electrons that occupy the same orbital and have opposite spins

parallel spin

electrons in different orbitals but same spin number

Electron Configuration

the pattern by which subshells are filled, as well as the number of electrons within each principal energy level and subshell; can be abbreviated by placing the noble gas that precedes the element of interest in brackets

Aufbau (building-up) principle

Electrons fill from lower- to higher-energy subshells

n + l rule

the lower the sum of the values of the first and second quantum numbers, n + l, the lower the energy of the subshell.

Hund’s Rule

within a given subshell, orbitals are filled such that there are a maximum number of half-filled orbitals with parallel spins; due to electron repulsion; half-filled and fully filled orbitals have lower energies (higher stability) than other states

paramagnetic

Materials composed of atoms with unpaired electrons will orient their spins in alignment with a magnetic field, and the material will thus be weakly attracted to the magnetic field

diamagnetic

Materials consisting of atoms that have only paired electrons will be slightly repelled by a magnetic field

Periodic Table of the Elements (PT)

ordering of the known elements by atomic weights/number; reveals a pattern of periodically recurring physical/chemical properties

periodic law

the chemical and physical properties of the elements are dependent, in a periodic way, upon their atomic numbers

periods

rows of PT; 7 representing the first 7 principal quantum numbers; each element in a given period has one more proton and one more electron than the element to its left

groups/families

columns of PT; Groups contain elements that have the same electronic configuration in their valence shell and share similar chemical properties

may be named by Roman numeral of valence electrons and split into A/B classes OR 1-18 (modern IUPAC stanadard)

valence shell

outermost shell of electrons

valence electrons

The electrons in the valence shell, farthest from the nucleus and having the greatest amount of potential energy; can form bonds with valence electrons of other atoms

A/representative elements

valence electrons in s or p subshells

IA - VIIIA

B/nonrepresentative elements

include both the transition elements and the lanthanide and actinide series; may have unexpected electron configurations

transition elements

have valence electrons in the s and d subshells; can have multiple oxidation states due to losing different numbers of s and d electrons

(Groups IB-VIIIB/3-12)

some (Cu, Ni, Ag, Au, Pd, Pt) are particularly nonreactive

lanthanide and actinide series

have valence electrons in the s and f subshells

metals

lustrous solids* with high melting points, high densities^; can be deformed without making; good conductors

low effective nuclear charge, low electronegativity (high electropositivity), large atomic radius, small ionic radius, low ionisation energy, low electron affinity

left and middle of PT

*except mercury (liquid @ RT)
^excpet lithium (half that of water)

lustrous

shiny

malleability

ability of metal to be hammered into shapes

ductility

ability to be pulled or drawn into wires

oxidation states

charges when forming bonds with other atoms

conductor

can transmit heat and electricity

i.e. metals are good conductors because of their loose, free-moving valence electrons

active metals

valence electrons found in s subshell

do not exist naturally in neutral forms; always found in ionic compounds/minerals/ores

nonmetals

brittle and dull when solid; poor conductors; less unified in chemical and physical properties than metals

high electronegativity (low electropositivity), small atomic radius, large ionic radius, high ionisation energy, high electron affinity

upper right of PT

*except mercury (liquid @ RT)
^excpet lithium (half that of water)

metalloids/semimetals

physical properties vary widely

chemical properties between metals and nonmetals; reactivities depend on elements with which they are reacting

staircase btwn metals and non-metals (B, Si, Ge, As, Sb, Te, Po, At)

effective nuclear charge (Zeff)

electrostatic attraction between the valence shell electrons and the nucleus

increases along period; largely stable along group

noble (inert) gases

have a full octet; minimal chemical reactivity; high ionisation energies and no measurable electronegativities

Group VIIIA/18

atomic radius

equal to one-half of the distance between the centers of two atoms of an element that are briefly in contact with each other

decreases along period; increases along group

ionic radii

1. metals lose electrons and become positive, while nonmetals gain electrons and become negative

2. metalloids can go in either direction, but tend to follow the trend based on which side of the metalloid line they fall on. (Si behaves more like a nonmetal, while (Ge) tends to act more like a metal)

non-metal ions closest to metalloid staircase are largest
metal ions closest to metalloid staircase are smallest

Ionization energy (IE)/ionization potential

energy required to remove an electron from a gaseous species

subsequent removals will require increasing amounts of energy

increases along a period, decreases along a group

Electron affinity

to the energy dissipated by a gaseous species when it gains an electron (reported as a positive number)

increases along a period; decreases along group

Electronegativity

measure of the attractive force that an atom will exert on an electron in a chemical bond

increases along a period; decreases along group

Alkali metals

possess most of the classic physical properties of metals, except that their densities are lower than those of other metals; only one loosely bound electron in their outermost shells - form monovalent cations

Group IA/1

Alkaline earth metals

possess most of the classic physical properties of metals; two electrons in their outermost shells - form divalent cations

Group IIA/2

Chalcogens

eclectic group of nonmetals and metalloids; some are crucial for normal biological functions, the rest are metallic and toxic, and all are toxic in high doses

Group VIA/16

Halogens

highly reactive nonmetals with seven valence electrons; multiple states of matter; so reactive only found as ions or diatomic molecules

Group VIIA/17

halide

anion of halogens

hydration complexes

complex ions interactions with water

compex ions

Any ion in which a central metal atom (normally a transition element) is surrounded by a group of ions or molecules (ligands)

known for varied bright colors; absorbs certain frequencies of light

subtraction frequencies

light reflected or not absorbed by an object that gives the object its color

complementary color to the frequency that was absorbed

complementary color

‘opposite’ colour, as in a colour wheel

Maillard reaction

a nucleophilic reaction between the amino terminus of the peptide chain of a protein and the carbonyl functionality of a sugar to form an N-substituted glycosylamine; a complex series of rearrangements and other reactions to produce a set of compounds that gives cooked food its pleasing color and delectable flavor

ex. browning meat, crisping cookies

molecules

combinations of bonded atoms

chemical bonds

strong attractive forces between atoms in a molecule formed via the interaction of the valence electrons of the combining atoms

octet rule

an atom tends to bond with other atoms so that it has eight electrons in its outermost shell, thereby forming a stable electron configuration similar to that of the noble gases

Incomplete octet

stable with fewer than 8 electrons in their valence shell

• hydrogen (2 electrons)

• helium (2)

• lithium (2)

• beryllium (4)

• boron (6)

Expanded octet

Any element in period 3 and greater can hold more than 8 electrons

• phosphorus (10)

• sulfur (12)

• chlorine (14)

Odd numbers of electrons

Any molecule with an odd number of valence electrons cannot distribute those electrons to give eight to each atom

ex. nitric oxide (NO) has eleven valence electrons

common elements that almost always abide by the octet rule

carbon, nitrogen, oxygen, fluorine, sodium, magnesium

ionic bonding

one or more electrons from an atom with a low ionization energy, typically a metal, are transferred to an atom with a high electron affinity, typically a nonmetal; difference in electronegativity must be greater than 1.7 on the Pauling scale

ionic crsytalline lattice

repeating rows of cations and anions; attractive forces between oppositely charged ions are maximized, and the repulsive forces between ions of like charge are minimized

covalent bonding

an electron pair is shared between two atoms, typically nonmetals, that have relatively similar values of electronegativity