TOPIC 2

Question 1

Atomic Theories

Answer 1

Dalton
1803

Thompson
1904

Rutherford
1911

Bohr
1913

Schrödinger
1926

Question 2

Rutherfords gold foil experiment

Answer 2

Rutherford recalled that “it was as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you”

He shot a beam of alpha particles coming from a radioactive source at a sheet of gold foil, and a with a detector identified that some of the particles were deflected by small angles, indicating a small concentrated positive charge; he concluded that a small, dense nucleus (positively charged) was causing the deflections.

Question 3

Mass number and Atomic number

Answer 3

Atoms of and element are characterized by 2 numbers

A = Mass Number = p+ + n• = number of nucleones (particles in the nucleus of the atom)

Mass number A can only be given for an atom of an element (not an element as a whole) and must always be a whole number.

Z = Atomic Number = p+ = position of an element in the P.T. = nuclear charge

Question 4

Atoms are…

Answer 4

Neutral.
This means that they have the same amount of p+ and e-

Question 5

Relative mass and charge of e-, p+ and n•

Answer 5

p+ n• e-
Relative mass 1 1 0
Charge +1 0 -1

No unit, its mass in comparison with themselves.
The e- has mass, because its matter, but in comparison to the p+ and n• its nearly neutral.

Question 6

Ions

Answer 6

Ions are formed when the number of p+ in an atom is no longer balanced by the number of e- in the atom.
They are chemically charged elements

When an atom loses e-, a + ion is formed
- cation

When an atom gains e-, a - ion is formed
- anion

Question 7

Isotopes

Answer 7

Atoms of the same element with different mass number

They have the same atomic number, and the same chemical properties, but different number of n• and different physical properties.

Question 8

Mass number (Ar)

Answer 8

Mass number is called the relative atomic mass of an element (Ar).

The Ar of an element takes into account the relative abundances of its isotopes.

“The Ar of an element is the average of its isotopes, considering their abundances.”

Question 9

Ar = ?

Answer 9

Ar = A x %abundance / 100

A = mass number

Question 10

Schrödinger’s model of the atom

Answer 10

He introduces atomic orbitals: an atomic orbital is a region around the nucleus in which we are most likely to find and e- (95% - 99%)

ORBIT AND ORBITAL ARE DIFFERENT
(Orbit is a fixed path [main energy level’s - Bohr’s model of the atom])

Schrödinger stated that e- do not move in set paths around the nucleus, but in waves. Its impossible to know the exact location of an e-; instead, we have “clouds of probability ” calles orbitals, in which we are more likely to find e-

Question 11

Atomic orbitals characteristics

Answer 11

Any orbital can hold a maximum of two e- of opposite spin.
Atomic orbitals are found within a specific energy sub-level, within a main energy level.

Question 12

Main and Sub energy levels

Answer 12

Types of sub-levels
S: 1 orbital: 2e- max
P: 3 orbitals: 6e- max
D: 5 orbitals: 10e- max
F: 7 orbitals: 14e- max

Main energy levels
1) 2e- max
s: 2e-
2)
8e- max
s: 2e-
p: 6e-
3) 18e- max
s: 2e-
p: 6e-
d: 10e-
4) 32e- max
s: 2e-
p: 6e-
d: 10e-
f: 14e-
5)
s
p
d
f
n)
…

For the same main energy level ‘n’, the energy of the sub-levels increases as s<p<d<f

Question 13

“Rule of rain”

Answer 13

Oder in which we fill the orbitals and sub-levels

(Tabla)
Num: main energy level (Bohr)
Letter: energy sub-levels (Schrödinger)

1s
2s 2p
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d 5f
Increasing energy—>

As the e- jumps away from the nucleus, the electromagnetic force of attraction towards it decreases. As a result, it become less stable, therefore accounting for a higher energy.

Question 14

e- configuration

Answer 14

Full ground state (normal e- configuration- no excited e-)

Condensed (use the noble gas previous to the element to reduce the configuration, then continue until reaching the element on the P.T.)

Question 15

e- configuration of ions

Answer 15

When + ions are formed, we first remove e- with the highest energy (highest main energy level)

The e- configuration of - ions is determined by simply adding the e- into the next available electron orbital.

Question 16

Orbital diagrams

Answer 16

Atomic orbitals are represented as “boxes”, each holding a maximum of 2e- of opposite spin.

The spin of the e- is indicated via an arrow. Each half-arrow represents an e-

s: 1 box
p: 3 boxes
d: 5 boxes
f: 7 boxes

Question 17

Rules for filling in atomic orbitals

Answer 17

1) Aufball principle: e- are placed into orbitals of lowest energy level first
2) Pauli exclusion principle: two e- cannot occupy the same orbitals unless they have opposite spins.
3) Hund’s rule: when filing orbitals of equal energy (same main and sub energy level), the e- fill the orbitals singly first to avoid repulsion.

Question 18

e- configuration exceptions

Answer 18

Exceptions:
Cu: [Ar] 4s1 3d10
Cr: [Ar] 4s1 3d5

These exceptions are a consequence of the seem of stability from Cr and Cu.

Cr: the configuration 4s1 3d5 is better (more stable) than 4s2 3d4, as it foes not have e- — e- repulsion from 4s.

Cu: the configuration 4s1 3d10 is better (more stable) than 4s2 3d9 as the sub-level 3d is more attracted to the nucleus (4s is farther from the nucleus than 3d).

Question 19

Degenerate orbitals

Answer 19

Orbitals of equal energy (same main and sub energy levels)

2px, 2py, 2pz

Question 20

Shapes of orbitals

Answer 20

s
O

p
(Infinito)
px (infinito horizontal)
py (infinito vertical)
pz (sale de dimensión/ para ‘adelante’)

Question 21

Spectra

Answer 21

Electromagnetic (EM) radiation comes in different forms of differing energy. Together they make up the EM spectrum.

R.w M.w IR [visible] UV X-rays Gama-rays
————————————————> E, f
Wavelength <————————————

Energy is directly proportional to frecuency

Energy is inversely proportional to wavelength.

Question 22

Continuous and discrete spectrum

Answer 22

The continuous spectrum is the visible region of the EM spectrum. It contains all the colors which together make up white light (w.l. is a mixture of light waves of differing wavelengths or colors)

The discrete/line spectrum is characteristic to each element and only has certain light waves present (only certain colors will appear when the photon emitted by the e- of that element falls into the visible region of the EM spectrum)

e- are found in discrete (particular/specific energy) energy levels outside the atoms nucleus

In the context of the atomic spectra we will be always working with Bohr’s model of the atom.

Question 23

e- changing energy levels

Answer 23

e- can move to a higher energy level (excited state) by absorption of a photon. Similarily, e- can move from an excited state to a lower energy level by emitting a photon.

If the photon emitted by an e- as it falls to a lower energy level has an energy wave within the visible region of the EM spectrum, we will interpret it as a specific color.

Photon: a particle of light (dual particle-wave behavior of light)

Question 24

Bohr model of the atom and why we use it in atomic spectra

Answer 24

In Bohr’s model of the atom, energy levels are discrete and converge towards increasing energies.
(Drawing)

In atomic spectra we work with Bohr’s model of the atom because e- transitions between energy sub-levels (Schrödinger) can not be distinguished with precision, at least for now.

Line spectra are evidence of e- being found on discrete energy levels. If this were not true, the absorption spectrum would consist in all black, and the emission spectrum would be the same as the continuous spectrum.

Question 25

e- transitions in an H atom

Answer 25

Emission Absorption
nf radiation ni radiation
1 UV 1 UV
2 vis 2 vis
3 IR 3 IR

Question 26

Valence e-

Answer 26

The total number of e- in the outer main energy level (we must add up all the e- located in the outer main energy level, independently from their sub-level)

The group number of an element indicates its valence e-
Example: Be belongs to group 17 —> 7 valence e-

Question 27

Emission and Absorption spectrums

Answer 27

Emission spectrum:
When an e- moved from higher to lower energy levels.

Absorption spectrum:
When and e- moves from lower to higher energy levels.

Question 28

Ground state

Answer 28

Energy level an e- normally occupies (not excited)

Question 29

Wavelengths

Answer 29

“Longer wavelength” = less energy
“Shorter wavelength” = more energy