Unit 2 - Atomic Structure

400 BC - Democritus

• everything is related because everything is made up of atoms

• matter cannot be divisible past an atom, the atom is the smallest

1803 - John Dalton (5 key ideas)

1. atoms make up everything

2. *Atoms of the same element are all the same (didn’t know about isotopes)

3. atoms of different elements are different

4. atoms combine in whole number ratios

5. compounds are formed by joining two or more atoms

6. *atoms are indivisible and indestructible

Black box demo

indirect measurement - measuring the thickness of a book page by measuring the thickness of a book and dividing by the number of pages

Aristotle’s four element theory

Air, water, fire, earth

1880s - JJ Thompson

Discovered the electron using cathode ray experiments, demonstrating that atoms are divisible.

- Proposed the "plum pudding model" of the atom, where negatively charged electrons (the "plums") were embedded in a positively charged sphere (the "pudding").

• knew there needed to be something positively charged, just didn’t know what it was

1895 - Wilhem Roentgen

• discovers x-rays, high energy electromagnetic radiation that can penetrate soft tissue but is blocked by the bone

  • Used first to image feet for cobblers to make shoes

1897 - Henri Becquerel

• discovers radioactivity

  • had a device that could pick up ionizing radiation, radiation that creates ions in the air around a radioactive substance

1905 - Albert Einstein

photo-electric effect

Photo-electric effect

• When you add energy to densely packed atoms, something has to give → since protons are dense, they’ll stay but electrons will change

  • Theory = electron moves from ground state to excited state when energy is added, so when they go back to the ground state, they produce photons

  • More electrons are excited → more photons

  • Ex: copper over a flame shines green light because Cu has # of electrons in the middle of the periodic table, and green is in the middle of ROYGBIV

photon

particle of light

quanta

bundles of light

1911-12 - Ernest Rutherford

gold foil experiment:

• radioactive source that spewed high speed alpha positively charged particles

• went through a hole in the lead focusing plate

• detecting screens showed the path of the alpha particles on a zinc sulfide screen

• then, the beam went through gold foil, which is 10k atoms thick

• finally, a final detecting screen was used to detect the scattering of the particles after going through the foil

Conclusions:

• atoms are made up of mostly space

  • went/cut through gold atoms, didn’t go around them

• center (nucleus) is very small and dense

• nucleus is positively charged, specifically protons

  • DISCOVERED PROTONS

1915 - Henry Moseley

Decided to order elements based on their increasing atomic number

1920s - Neils Bohr

planetary orbit model

• theory: electrons orbit the nucleus like how the planets orbit the sun

• flaw: planetary orbits are all on a 2D plane, but atoms aren’t 2D and electrons never return to the same place

figured out that electrons that are furthur out have more energy and electrons spin a certain distances (energy levels) from the nucleus in 3D

electron cloud

electrons move so fast that you can’t even see them, you only see a cloud

1930s - James Chadwick

• discovers neutron, neutrally charged particle found in nucleus with roughly same size and mass and proton

• relative atomic sizes

1930s - Louis deBroglie & Max Planck

described duality of electrons

• they have properties of both waves and particles

• E = (h x c)/wavelength

  • h = Plank’s constant (relates energy of electron to its frequency, more frequency = more energy)

  • c = velocity of light

  • c and h are constant, so energy and wavelength are the only changing factors

• frequency and wavelength are indirectly prop.

• frequency and energy are directly prop.

• energy and wavelength are indirectly prop.

1930s - Shröedinger

8 variable equation that predicts location of single electron in Hydrogen (which only has 1 electron), and it only works for hydrogen

1930 - Heisenberg

uncertainty principle - if you know about an electron’s motion, you can’t know about its location. if you know about its location, you can’t know about its motion.

What are the four fundamental forces and who attempted to unite them into one force?

1. Gravity

2. Electromagnetism

3. Strong Force

   1. Weak force

Strong force

holds protons together in the nucleus and its strong because protons repel each other since they are both positive

weak force

weak force keeps protons and neutrons together

In a normal atom, why are there the same amount of protons as there are electrons?

Atoms are electrically neutral, so there must be an equal number of electrons as protons to balance the charges out

Cathode ray tude

In a tube, the electrons flowed between the positive and negative side of the battery. When a magnet was put against the tube with the negative side, the electron flow was repeled. When the positive side was placed next to the tube, the electron flow came close to the magnet, so that proved it was negatively charged

isotope

atoms are the same element, but there are a diff. # of neutrons

ions

atoms that lose or gain electrons

particle

individual atoms or individual molecules (2+ atoms chemically combined)

mole

the atomic weight of an element

if 3 substances are 1 mole, but all weigh different, it’s because…

they have a different number of protons/neutrons/electrons

avogadro’s number

6.023 × 10^23

how many energy levels are there?

7 levels

what are the four sublevels in an atom?

s, p, d, f

orbital

lanes in each sublevel (s:1, p:3, d:5, f:7)

how many max. electrons are in each lane in sublevels?

2

formula for total electrons in energy level

2n², n = level

aufbau

to build upon (a nucleus)

octet rule

atoms with an octet are noble gasses. atoms that have an octet (s²p^6) are very stable, but atoms that are one electron away are super reactive, trying to get the last electron

elements in the same colum are related because they have the same number of ____

valence electrons (outermost s and p electrons)

why is there stealing for Cr and its column?

there are 4 electrons in a row in the d lanes, and two in a colum in the s lane. The electrons prefer an even spread, so the bottom electron in the s lane is pulled over to the fifth lane. so, Cr is [Ar]4s^13d^5

why is there stealing for Cu and its column?

there’s a bigger preference for being fully filled, so copper takes and electron from ‘s’ for all 10 d lanes, resulting in [Ar]4s^13d^10

In orbital notation, what is the order of filling each circle?

for p, OOO, you do one electron in each circle before going back and making crosses in both

Hund’s Rule

electrons spread out in available orbitalsPa

Pauli’s Exclusion principle

2 electrons max. per orbital

[Core]

used as a shortcut by indicated all previously filled sublevels always with a previous energy level’s noble gas element as the core

quantum numbers/values

first way of electron arrangement, uses electron zipcode to represent ONE electron

n = energy level (1,2…7)

l = sublevel (s=0, p=1, d=2, f=3)

m = # of orbitals/lanes (l = 1 → (-1)-(0)-(1))

s = spin ( / → +1/2, X → -1/2)

what is helium (He) in quantum numbers

(1, 0, 0, -1/2)

shape of s orbital

spherical

shape of p orbital

peanut

shape of d orbital

double peanut

shape of f orbital

flower

modern atomic theory

all matter is made up of atoms, which have protons + neutrons in the nucleus and electrons forming a cloud around the nucleus

subatomic particle

protons, neutrons, electrons.

proton mass + neutron mass = very similar

proton mass + electron mass = protons are much heavier and much more dense

Moseley’s law

experiment = bombarded elements with electrons so they would emit characteristic x-rays

found: square root of x-ray frequency is proportional to the atomic number

proved: atomic number is the way to order elements, not atomic weight

Nuclide

An atom characterized by a specific number of protons and neutrons in its nucleus.

atomic weight

average definite mass, average of all masses from isotopes

angstrom

1 A = 10^-8 cm