Chemistry Unit 2 Test

Democritus

Democritus

• developed the first idea of the atom

• half of a glass of water: will there be a point where the water won’t be water any more?

• philosophical idea

John Dalton

• assumed the lowest ratio of atoms is 1:1

• studied the idea of atoms (experimentally)

• developed Atomic Theory

John Dalton’s Atomic Theory

1. atoms exist and are indivisible (needs revision)

2. each element had identical atoms, which are different from those of any other element (needs revision: isotopes)

3. Atoms physically mic, or chemically combine in whole # ratios to form compounds (correct)

4. chemical reactions are rearranging which atoms are combined, not changing the atoms

JJ Thomson

• discovered the electron

• high voltage can be passed through metal in a vacuum (cathode ray tube) → atoms are divisible

• Plum Pudding Model

Plum Pudding Model

• Thomson

• atom is a uniform, positive charge

• electrons embedded regularly within it

• no nucleus

Saturnian Model

• Nagaoka

• The positive charge is at the center, and electrons move around like Saturn’s rings

• energy would have been lost

Earnest Rutherford

• discovered the nucleus

• gold foil experiment:

  • positive charge in atom is super, super small (nucleus) but very heavy

James Chadwick

• discovered the neutron

• nobel prize

Which Subatomic Particle?

• Red- proton

• Purple- neutron

• Green- electron

Structure of an Electron

• location: outside nucleus

• mass: 1/1840 amu

• charge: -1

Structure of a Proton

• location: nucleus

• mass: 1 amu

• charge: +1

Structure of a Neutron

• location: nucleus

• mass: 1 amu

• charge: 0

Nucleus of an Atom

high mass, low volume

Structure of an element

• Proton: changes element

• Neutrons: changes mass/ isotope

• Electrons: changes charge (ions)

Atomic #

# of protons in an atom of the element

Mass #

# of protons + neutrons in an atom of the specific isotope

Element Symbol

Naming Isotopes

element-mass#

ex: oxygen-16 ion (3+)

Atomic Spectrum

• “finger print” of an element

• atoms get energy from the sun (exciting) and release it as light

• enables the identification of elements

The Photoelectric Effect

light has wave-particle duality

Photons

packets of waves

wave properties

wavelength: determines color+energy

particle properties

photons

Wavelength

• smaller wavelength→ faster electrons

• there is a cut off wavelength above which no electrons are released → depends on element

Photon Flux (brightness/frequency)

• # of protons determines how many electrons are released (1 electron→ 1 photon)

• does not impact speed of electron

Frequency + Wavelengths of light

Energy of a Photon

Niels Bohr

discovered that electrons orbit the nucleus in specific radius orbits of specific energies

Bohr Model

• electrons orbit the nucleus in specific radius orbits of specific energies

• quantized: only certain values are allowed

• ground state: n=1

• n = ∞: electron has left the atom

Absorption line spectrum

absorbed colors are absent

arrows pointing up

Emission line spectrum spectrum

emitted colors are present

arrows pointing down

ionization

n=1 → n=∞

absorption

n=2 → n=3,4,5…

Quantum Mechanical Model

• Schrödinger

• probability based

  • electron energy is quantized

  • electrons have wave-particle duality

orbital

area in which there is a 90% chance of finding an electron

s orbitals

• spherical

• origin: nucleus

• 1s 2s 3s: principal energy level

p orbitals

• energy levels 2 and above

• 3 p orbitals: p_z p_x p_y

d and f orbitals

5 d orbitals, principal energy levels 3 and above

7 d orbitals, principal energy levels 4 and above

electron configurations

arrangement of electrons in an atom

orbital filling diagram

The Aufbau Principle

electrons enter orbitals of lowest energy first

Pauli Exclusion Principle

no 2 electrons have the exact same energy state

electrons have a quantum property called spin

max of 2 electrons in an orbital, must have opposite spin

Hund’s Rule

when electrons occupy orbitals of equal energy, they do so to maximize the overall spin

weighted average formula

avg=(mass₁ x percentage₁) + (mass₂ x percentage₂)

higher energy transitions are associated with high frequency, shorter wavelength light

higher energy transitions are associated with high frequency, shorter wavelength light

define atom

building blocks of matter

excited state

when n increases

spin

rotation of electrons