ACS EXAM review

Rutherford's Gold Foil Experiment

proposed that atoms consist of a tiny, massive, positive nucleus surrounded by electrons

nucleus

contains all the positive charge and nearly all the mass of the atom

James Chadwick

discovered the neutron

cathode rays

move from negative electrode to positive electrode (like electrons in a voltaic cell)

Thompson's Cathode Ray Experiment

discovery of the electron (also the discovery that atoms are divisible into smaller particles)

Millikin's oil drop experiment

determined the charge of the electron through highest grade clock oil and electrons from X-ray that clung to positive charged oil drops- determined that electrons are some whole value of charge (Faraday constant)

Thompson's plum pudding model

model of a spherical atom composed of diffuse positively charged matter in which electrons are embedded like raisins in plum pudding

atomic number

number of protons (Z)

mass number

number of protons and neutrons (nucleons) (A)

isotopes

same element with different numbers of neutrons

mass spectrometry

a method for measuring the relative masses and abundances of atomic scale particles very precisely

empirical formula

shows relative number of atoms in a compound

molecular formula

shows the actual number of atoms of each element in a molecule of compound

aufbau principle

the rule that electrons occupy the orbitals of lowest energy first

quantum mechanics

mechanics applied to the atomic and nuclear level and dealing with photons and other quanta that show both wave and particle behavior

Heisenburg's uncertainty principle

the statement that, due to the laws of quantum mechanics, it is impossible to simultaneously exactly measure a particle's position and momentum or to exactly measure a particle's energy for a finite amount of time.

electron energy

The strength of attachment of an electron to the nucleus of an atom; the closer and electron to the nucleus, the higher the electron binding energy.

quantum numbers

the four numbers that define each particular electron of an atom. The Principle Quantum Number (n) describes the electrons' energy and distance from the nucleus. The Angular Momentum Quantum Number (l) describes the shape of the orbital in which the electron resides. The Magnetic Quantum Number (m) describes the orientation of the orbital in space. The Spin Quantum Number (s) describes whether the spin of the electron is positive or negative.

photon

packet of energy

electromagnetic radiation

A form of energy exhibiting wavelike behavior as it travels through space; can be described by wavelength, frequency, amplitude, and speed.

radial probability distributions

a graph in which the total probability of finding the electron in each spherical shell is plotted versus the distance from the nucleus

isoelectronic

same number of electrons

group 1

alkali metals

group 2

alkaline earth metals

group 7

halogens

group 8

noble gases

electromagnetic spectrum (decreasing energy)

x-ray, uv-ray, visible light, infrared light, microwaves, tv, radio waves

higher photon energy

higher frequencies (∨) and shorter wavelengths (λ)

speed of light (c)

3.00 x 10⁸ ms⁻¹, maximum speed of any and all motion; electromagnetic waves travel at this speed

principal quantum number (n)

a positive integer (1,2,3,etc.) that indicates the relative size of the orbital and therefore the relative distance from the nucleus of the peak in the radial probability distribution plot. The higher the n value, the higher the energy level.

angular momentum quantum number (l)

an integer from 0 to n-1. It is related to the shape of the orbital. (notice that n limits l) (the possible number of l values equals the number of n)

quantum number (ml)

an integer from -l through 0 to +l. It prescribes the orientation of the orbital in the space around the nucleus. (number of possible ml= 2l+1)

quantum number (ms)

direction of spin (+1/2 or -1/2)

hund's rule

electrons in orbitals of the same energy do not pair until they have to

atomic line spectra

(further explanation) provide evidence that the energy state of an electron in an atom is quantized

absorbed

energy must be ______ for an electron to move from one energy state in an atom to another energy state that is more remote from the nucleus

emitted

energy must be _____ for an electron to move from one energy state in an atom to another energy state that is closer to the nucleus

paramagnetism

exhibited by a species with unpaired electrons

diamagnetism

exhibited by a species with all electrons paired

allotrope

a structurally different form of an element; graphite and a diamond have the same formula but different structure to the atoms

isomer

compounds that have the same simple formula but different three-dimensional structures

polymer

large compound formed from combinations of many monomers

s sublevel

l=0 (spherical)

p sublevel

l=1 (dumbbell shape)

d sublevel

l=2 (clover shape/dumbbell and do-nut)

f sublevel

l=3

Valence Electron Pair Repulsion (VSPER) Theory

each group of valence electrons around a central atom is located as far away as possible from others in order to minimize repulsion

ionization energy

energy required for the complete removal of 1 mol of electrons from 1 mol of gaseous atoms or ions (increases across a period, decreases down a group)

electron affinity

energy change accompanying the addition of 1 mole of electrons to 1 mol of gaseous atoms or ions (EA₁ is usually negative: releases energy, EA₂ is always positive: requires energy to overcome electrostatic repulsions)

high energy photons

have enough energy to disrupt covalent bonds

low ionization energy

readily lose electrons to form positive ions

high electron affinity

readily gain electrons to form negative ions

ionic bonds

result when atoms exchange electrons

covalent bonds

result when atoms each contribute an electron to a shared pair

coordinate covalent bonds

result when one atom contributes two of its electrons to a shared pair

metallic bonds

result when atoms free one or more valence electrons to the metal lattice

properties of ionic compounds

hard, high melting; conduct a current only when melted or dissolved; strong intermolecular attractions

properties of covalent compounds

low melting and boiling points; weak intermolecular attractions

properties of metallic compounds

metallic behavior correlates with large atomic size and low ionization energy (increases down a group and decreases across a period)

properties of covalent network solid compounds

very hard and big melting; covalent bonds throughout the substance (diamond=hardest known natural substance)

electronegativity

relative ability of a bonded atoms to attract the shared electrons

electromagnetic radiation

consists of energy propagated by electric and magnetic fields that alternately increase and decrease in intensity as they move through space

frequency

(∨) number of cycles the wave undergoes per second and is expressed in hertz (units of s⁻¹)

wavelength

(λ) distance between any point on a wave and the corresponding point on the proximate wave; distance wave travels during one cycle; (measured in meters. but also expressed in pico (10⁻⁹) and femto (10⁻¹²) meters and Angstroms (10⁻¹⁰)

amplitude

height of the crest for each wave; related to the intensity of the wave

c = ∨ x λ

formula for speed of wave

electromagnetic spectrum

all waves in the _____ travel at the same speed but differ in frequency and wavelength

gamma ray, x-ray, uv-ray, visibile, infrared, microwave, radio

electromagnetic waves in order of decreasing frequency

refraction

the phenomenon that describes when light passes from one medium into another, its speed changes (the wave will continue at a different angle)

diffraction

the phenomenon that describes when a wave strikes the edge of an object, it will bend around it

interference

if waves of light pass through adjacent slits, the emerging circular waves interact with each other

constructive interference

when crests of waves coincide in phase and the amplitudes add together

destructive interference

when the crests of one wave coincides with the troughs of another wave and the amplitudes cancel

blackbody radiation

light given off by a hot blackbody that led to Max Plank's quantization of energy in his equation E= nhv (later it followed that if an atom can only emit certain quantities of energy, then an atom can only have certain quantities of energy- photons)

6.626x10⁻³⁴

Plank's constant

quantum

defined amount of energy (energy packet)

photoelectric effect

the flow of current when monochromatic light shines of sufficient frequency (minimum value/threshold) shines on a metal plate

photons

(acc. to Einstein) light is quantized into small bundles of electromagnetic energy called ______. (also called quanta)

atomic line spectrum

a series of fine lines of individual colors separated by colorless (black) spaces (each species has a characteristic spectrum)

1/λ=R (1/n₁²-1/n₂²)

Rydberg equation (R=1.0968x10⁷ m⁻¹)

Bohr model of the hydrogen atom

1. H atom has only certain allowable energy states (stationary states)

2. atom does not radiate energy while in one of its stationary states (atom does not change energy while the electron moves within an orbit)

3. the atom changes to another stationary state only by absorbing or emitting a photon whose energy equals the difference in energy between the two states

H He⁺

bohr model is only successful in explaining the electron behavior of ____ and ____, which have only one electron

-2.18x10⁻¹⁸(1/n²final- 1/n²initial)

∆E (for energy levels)=

(more negative= more energy= electron is further from the nucleus)

de Broglie wavelength

matter behaves as though it moves in a wave (an object's wavelength is inversely proportional to its mass)

electron density diagram

(radial probability distribution plot) probable distribution of electrons around an atom in an electron cloud shown through Schrodinger's model

Pauli Exclusion principle

no two electrons in the same atom can have the same four quantum numbers

Coulomb's Law

electric force between charged objects depends on the distance between the objects and the magnitude of the charges.

electrons penetrate

the lower an l value the more ____

s

order of sub level energies

decreases; increases

atomic radius ______ from left to right and ______ from top to bottom

large jump in ionization energy (IE)

after the outer valence electrons have been removed, there is a _______

smaller

cations are ___ than their parent atoms