A beryllium atom has 4 protons, 5

neutrons, and 4 electrons. What is the

mass number of this atom?

a) 4

b) 5

c) 8

d) 9

e) 13

Atomic structure

The smallest particle into which an element can be

divided and still have the properties of that

element

a) nucleus

b) electron

c) atom

d) neutron

How would you describe the nucleus?

a) dense, positively charged

b) mostly empty space, positively charged

c) tiny, negatively charged

d) dense, negatively charged

Atomic structure

Where are electrons likely to be found?

a) in the nucleus

b) in electron clouds

c) mixed throughout an atom

d) in definite paths

Every atom of a given element has the same

number of

a) protons

b) neutrons

c) electrons

d) isotopes

Atomic structure

What is the meaning of the word atom?

a) dividable

b) invisible

c) hard particles

d) not able to be divided

Which statement is true about isotopes of the

same element?

a) They have the same number of protons

b) They have the same number of neutrons

c) They have a different atomic number

d) They have the same mass

Atomic structure

Which has the least mass in an atom?

a) nucleus

b) proton

c) neutron

d) electron

If an isotope of uranium, uranium-235, has 92

protons, how many protons does the isotope

uranium-238 have?

a) 92

b) 95

c) 143

d) 146

Atomic structure

A carbon atom with 6 protons, 6 electrons, and 6

neutrons would have a mass number of

a) 6

b) 12

c) 15

d) 18

The number at the top is the

a) atomic number

b) element name

c) atomic mass

d) chemical symbol

Atomic structure

How many electrons does a neutral Cl atom

contain?

a)16

b)17

c)18

d)19

What is the difference between atomic mass and

atomic weight?

Atomic structure

Atomic Structure

Neutral atoms have the same number

of protons and electrons.

Ions are charged atoms.

●cations – have more protons than

electrons and are positively charged

●anions – have more electrons than

protons and are negatively charged

If a neutral atom looses one or more electrons

it becomes a cation.

If a neutral atom gains one or more electrons

it becomes an anion.

Na 11 protons

11 electrons Na+ 11 protons

10 electrons

Cl 17 protons

17 electrons Cl- 17 protons

18 electrons

Atomic Structure

e- +

+ e-

electrons are assumed to

revolve around the atomic

nucleus in discrete orbitals,

and the position of any

particular electron is more

or less well defined in terms

of its orbital.

Electrons are permitted to

have only specific values of

energy.

Bohr Atomic model

Bohr Atomic model

excitation vs relaxation

An electron may change

energy by making a quantum

jump either to an higher

energy (with absorption of

energy) or to a lower energy

(with emission of energy).

excitation relaxation

Quantum Mechanics

Unfortunately, extremely small particles

(electrons) do not follow the laws of classical

(Newtonian) physics. The new physics that

mathematically treats small particles is called

Quantum Mechanics.

electron distribution

wave-mechanical model

an electron is no longer treated

as a particle moving in a discrete

orbital;

electron is considered to exhibit

both wavelike and particle-like

characteristics.

The position of an electron is

described by a probability

distribution // electron cloud.

Quantum Mechanics Wave behavior is described with the wave function

ψ, incorporating the wave and particle features of

electrons (Erwin Schrödinger)

The probability of finding an electron in a certain

area of space is

proportional to ψ2

electron density.

Austrian; 1933 Nobel

prize in physics

Quantum Mechanics

Heisenberg’s uncertainty principle more precisely the position of some particle is determined, the less precisely its momentum can be known

A macroscale analogy…

High Shutter Speed Low Shutter Speed

Can judge location, Can judge speed,

but not speed. But not location

we cannot precisely measure the momentum and

the position of an electron at the same time.

As the momentum of the electron is more and more

certain, the position of the electron becomes less

and less certain, and vice versa.

n = 2.5 cannot exist as a principal quantum number.

There must be an integral number of wavelengths

(n) in order for an electron to maintain a

standing wave. If there were to be partial waves,

the whole and partial waves would cancel each

other out and the particle would not move.

Heisenberg’s uncertainty principle

Quantum Mechanics The Schrödinger equation

specifies possible energy states

an electron can occupy.

The energy states and wave

functions are characterized by

a set of quantum numbers.

Instead of orbits in the Bohr

model, quantum numbers and

wave functions describe atomic

orbitals.

every electron in an atom is characterized by four

quantum numbers.

There are three quantum numbers necessary to

describe an atomic orbital.

The principal quantum number (n)

designates size

The angular moment quantum number (l)

describes shape

The magnetic quantum number (ml)

specifies orientation

quantum numbers

Principal Quantum Number (n)

designates the size of the orbital.

Larger values of n correspond to larger orbitals.

The allowed values of n are integers: 1, 2, 3 and so

forth.

A collection of orbitals with the same value of n is

frequently called a shell.

n

K L M N O P .......

1 2 3 4 5 6 ……

Angular moment Quantum Number (l)

signifies the subshell

describes the shape of the orbital.

l values range from 0 to n – 1

Example: If n = 2, l can be 0 or 1.

n 1 2 3 4 5 6

l

subshell

0 1 2 3 4 5

s p d f g h

energy state 1 3 5 7 9 11

Magnetic Quantum Number (ml)

describes the orientation of the orbital in space.

ml are integers that depend on l: – l,…0,…+l

ml identifies # of energy states for each subshell

For an s subshell: a single energy state

For p, d, and f subshells: 3, 5, and 7 energy states

Principal

Quantum No: n

Shell

Subshell

l No. of energy States:

ml

Number of Electrons

Per Subshell Per Shell

1 K s /0 1 / 0 2

2

2 L s / 0 1 / 0 2

8 p / 1 3 / -1,0,+1 6

3 M s / 0 1 / 0 2

18 p / 1 3 / -1,0,+1 6

d / 2 5 / -2,-1,0,+1,+2 10

4 N

s / 0 1 / 0 2

32 p / 1 3 / -1,0,+1 6

d / 2 5 / -2,-1,0,+1,+2 10

f / 3 7 / -3,-2,-1,0,+1,+2,+3 14

5 O

s / 0 1 / 0 2

50 p / 1 3 / -1,0,+1 6

d / 2 5 / -2,-1,0,+1,+2 10

f / 3 7 / -3,-2,-1,0,1,2,3 14

g / 4 9 / -4,-3,-2,-1,0,+1,+2,+3,+4 18

6 P

s / 0 1 / 0 2

72

p / 1 3 / -1,0,+1 6

d / 2 5 / -2,-1,0,+1,+2 10

f / 3 7 / -3,-2,-1,0,1,2,3 14

g / 4 9 / -4,-3,-2,-1,0,1,2,3,4 18

h / 5 11 / -5,-4,-3,-2,-1,0,+1,+2,+3,+4,+5 22

Number of available electron states for initial shells and subshells

An s subshell has one orbital which is spherically

shaped.

If you were to measure where the electron was

within an s subshell many, many times and plot

the results on a graph you would get something

like this.

Atomic orbitals