Chemical Structure: Structure of Matter. Atoms – the building blocks of matter

This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License

Atoms – the building blocks of matter

University of Lincoln presentation

http://creativecommons.org/licenses/by-nc-sa/2.0/uk/

http://chemistryfm.blogs.lincoln.ac.uk/


What’s so special about atoms?

• All matter is made of atoms• When 2 surfaces touch each other,

atoms from one surface are transferred to the other

TRACE EVIDENCE



The Locard Principle of Exchange

Prof Edmond Locard (1877-1966)

“When objects come into contact there is a transfer of particles”…….



For example• FIREARM

DISCHARGE RESIDUE– When a firearm is discharged, traces of lead, antimony and barium are deposited onto the hand holding the gun.

• IDENTIFYING SITE OF BULLET PENETRATION– Uncoated lead bullets and copper-coated bullets discharged from firearms and penetrating wood, fabric, paper, etc., leave behind 0.1 – 100 micron particles of metallic lead or copper



What you Need to Know…

• Structure of the atom – proton, neutron and electron

• Electron orbitals – s- and p-orbitals, principal quantum numbers and energy

• Electronic configurations – noble gas configurations, core electrons and valence electrons

• Drawing energy level diagrams – putting electrons into orbitals and pairing electrons



Atomic Structure

The Bohr atom

Direction of electron motion

Nucleus

Electron



Make-up of the Atom

The NUCLEUSTwo particles make up the nucleus:o PROTONo NEUTRON

A third particle, the ELECTRON, moves around the nucleus in ORBITALS



The three atomic particles

PROTON NEUTRON ELECTRON

Charge (C) +1.602x10-19 0 -1.602x10-19

Charge number

+1 0 -1

Rest mass (kg)

1.673x10-27 1.675x10-27 9.109x10-31

Relative mass

1837 1839 1



Orbitals

Consider the moon orbiting the earth:

We always know where the moon is because we can see it – its position and motion can be defined EXACTLY

For an e- with a tiny mass, this is not the case – it is impossible to know, exactly, both its position and momentum at the same instant in time.

This is known as Heisenberg’s uncertainty principle



Orbitals

If we can’t determine exactly where the electron is, we must consider the probability of finding the electron in a given volume of space. This volume of space is called an ORBITAL

Probabilities are calculated mathematically, and in this case are defined by the

Schrödinger wave equation



Why do we need to know where the electrons are?

ElementMatter made up of

identical atoms

Atoms

Protons Neutrons Electrons

The element is defined by the

number of protons it has

The number of electrons= the number of protons

Position of the electrons within the atom defines

the chemistry of the element



Periodic Table of the Elements

f - block elements

H

BeLi

Na

K

Rb

Cs

Fr

Mg

Ca

Sr

Ba

Ra

Sc

Y

La

Ac

Ti V Cr Mn Fe Co Ni Cu Zn

Zr

Hf Ta W Re Os Ir Pt Au Hg Tl

Nb Mo Tc Ru Rh Pd Ag Cd In Sn

Pb Bi Po At Rn

Xe

Kr

Ar

Ne

Sb Te I

Ga

Al

Ge

Si P S Cl

As Se Br

Ce Pr Nd Pm Sm

Eu Gd Tb Dy Ho Er Tm Yb Lu

Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr

He

B C N O F

LanthanoidsActinoids

d – block elements

Hydrogen and s – block elements

p – block elements



The first 20 elementsElement Number of

protons (Atomic

number = Z)

Number of electrons

Na 11 11

Mg 12 12

Al 13 13

Si 14 14

P 15 15

S 16 16

Cl 17 17

Ar 18 18

K 19 19

Ca 20 20

Element Number of protons (Atomic

number = Z)

Number of electrons

H 1 1

He 2 2

Li 3 3

Be 4 4

B 5 5

C 6 6

N 7 7

O 8 8

F 9 9

Ne 10 10



Where are these electrons?

According to Schrödinger, there are 4 different types of orbital in an atom (each type has a different shape):

Orbital label

No. orbitals

No. e-s per orbital

Total no. e-s

s 1 2 2

p 3 2 6

d 5 2 10

f 7 2 14



Shapes of Orbitals (s & p)z

x

y

z

y

x

z

y

x

S-orbital

P-orbitals

z

y

x

Px Py Pz



Shapes of Orbitals (d)z

y

x

z

y

x

z

y

x

z

y

x

z

x

y

dyz dxy dxz

dz2 dx

2 y2

Note change of axis



Electron Orbitals

1s 2s 3s 4s 5s 6s 7s

2p 3p 4p 5p 6p

3d 4d 5d

4f 5f

The number is called the principal quantum number (n) and indicates the size of the orbital (1 is the smallest; 7 the largest)



The Principal Quantum Number

1s 2s 3s 4s

The increase in size of atomic orbitals



Position of Orbitals Around Nucleus

Nucleus

0

5

10

15

20

25

30

0 5 10 15 20

Distance from atomic nucleus (r, atomic units)

Pro

bab

ilit

y4πr2R(r)2

1s

2s3s

Energy increase



Relationship Between Principal Quantum Number and Energy

Energ

y, E 0

n = 1

n = 2

n = 3

n = 4

n = 5

n = 6

n = ∞ Energy levels

become closer together



Comparing the Energy for n=3

0

5

10

15

20

25

0 5 10 15 20 25

Distance from the nucleus (r,atomic units)

Pro

bab

ilit

y

3d3p

3s

4πr2R(r)2

Energy increase



The Energy of OrbitalsEnerg

y

1s

2s

3s

2p

3p

3d

N = 1

N = 2

N = 3

Each orbital will hold 2 electrons

Link to “Energy level diagrams”

video



How do the electrons fill these orbitals?

Groundstate electronic configurations:In order for an element to be stable, it has to house

its electrons in such a way that its overall energy is as low as possible

The electrons will therefore occupy the lowest energy orbitals available



Orbitals in energy order

1s 2s 3s 4s 5s 6s 7s

2p 3p 4p 5p 6p

3d 4d 5d

4f 5f

1s < 2s < 2p< 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p< 6s < 4f 5d

< 6p < 7s < 5f



Electronic Configuration Atomic number

Element Symbol

Electronic configuration

Atomic number

Element Symbol

Electronic configuration

1 H 1s1 11 Na 1s22s22p63s1

2 He 1s2 12 Mg 1s22s22p63s2

3 Li 1s22s1 13 Al 1s22s22p63s23p1

4 Be 1s22s2 14 Si 1s22s22p63s23p2

5 B 1s22s22p1 15 P 1s22s22p63s23p3

6 C 1s22s22p2 16 S 1s22s22p63s23p4

7 N 1s22s22p3 17 Cl 1s22s22p63s23p5

8 O 1s22s22p4 18 Ar 1s22s22p63s23p6

9 F 1s22s22p5 19 K 1s22s22p63s23p64s1

10 Ne 1s22s22p6 20 Ca 1s22s22p63s23p64s2



Three things to remember

1. For principal quantum numbers >1 there is both an s- and a p-orbital. This means 8 electrons are needed to fill these two orbitals. If the orbitals are all filled, the element is extra stable. These elements are the NOBLE gases

2. CORE electrons are those electrons sitting in filled orbitals. These usually correspond to the noble gas configurations (He, Ne, Ar etc.)

3. VALENCE electrons are the electrons outside the core electrons. It is these electrons that define the chemistry of the element



Noble gases: Group 18

Nob

le g

ases:

All

orb

itals

are

fille

d

H

BeLi

Na

K

Rb

Cs

Fr

Mg

Ca

Sr

Ba

Ra

Sc

Y

La

Ac

Ti V Cr Mn Fe Co Ni Cu Zn

Zr

Hf Ta W Re Os Ir Pt Au Hg Tl

Nb Mo Tc Ru Rh Pd Ag Cd In Sn

Pb Bi Po At Rn

Xe

Kr

Ar

Ne

Sb Te I

Ga

Al

Ge

Si P S Cl

As Se Br

Ce Pr Nd Pm Sm

Eu Gd Tb Dy Ho Er Tm Yb Lu

Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr

He

B C N O F



Energy Level Diagrams - Arrangement of Electrons in

Orbitals

Electrons remain unpaired when they can (i.e. when there is more than 1 orbital of the same energy)

Work out the number of electrons that are present, and then start filling the lowest energy orbitals first

En

erg

y

1s

2s2p

En

erg

y1s

En

erg

y

1s

2s

C He Li



How do electrons pair up?

In order to pair up, electrons have to spin in

different directions

= +ve spin = -ve spin

Incorrect Correct



Summary

• Structure of the atom – proton, neutron and electron

• Electron orbitals – s- and p-orbitals, principal quantum numbers and energy

• Electronic configurations – noble gas configurations, core electrons and valence electrons

• Drawing energy level diagrams – putting electrons into orbitals and pairing electrons



Acknowledgements

• JISC• HEA• Centre for Educational Research and

Development• School of natural and applied sciences• School of Journalism• SirenFM• http://tango.freedesktop.org