Chap 1 Atomic Structure

8/12/2019 Chap 1 Atomic Structure

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Atomic Structure

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Atomic StructureContent

I The nucleus of the atom: neutrons and protons, isotopes, proton and

nucleon numbers

II Electrons: electronic energy levels, ionisation energies, atomic orbitals,

extranuclear structure

Learning Outcomes:

identify and describe protons, neutrons and electrons in terms of

their relative charges and relative masses

deduce the behaviour of beams of protons, neutrons and

electrons in electric fields

describe the distribution of mass and charges within an atom

deduce the numbers of protons, neutrons and electrons present

in both atoms and ions given proton and nucleon numbers (and charge)

describe the contribution of protons and neutrons to atomic

nuclei in terms of proton number and nucleon number


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Atomic Structure distinguish between isotopes on the basis of different numbers

of neutrons present

describe the number and relative energies of the s, p and d

orbitals for the principal quantum numbers 1, 2 and 3 and also the 4s and 4p

orbitals.

describe the shapes of s and p orbitals

state the electronic configuration of atoms and ions given the

proton number (and charge)

explain and use the term ionisation energy

explain the factors influencing the ionisation energies of elements explain the trends in ionisation energies across a Period and down a Group of

the Periodic Table (see also Section 9)

deduce the electronic configurations of elements from successive ionisation

energy data

interpret successive ionisation energy data of an element in terms of the

position of that element within the Periodic Table


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ELEMENT

Pure substances that

contain atoms of only

one type.


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DaltonsAtomic Theory

All matter is composed of atoms

Atoms cannot be made or destroyed All atoms of the same element are identical

Different elements have different types of atoms

Chemical reactions occur when atoms are rearranged

Compounds are formed from atoms of the constituent

elements.

John Dalton(1766

1844)


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1898 J. J THOMPSON

Discovered atoms could sometimes eject a

far smaller negative particle which he called

an ELECTRON

Introduced Plum-pudding model whereby

the electron (plums) are embedded in a

sphere of uniform positive charge.


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1910 Ernest Rutherford

Rutherfords new evidence allowed him topropose a more detailed model with a centralnucleus.

He suggested that the positive chargewas all ina central nucleus. With this holding the electronsin place by electrical attraction


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1913 Niels Bohr

Bohr refined Rutherford's idea by

adding that the electrons were in orbits.

Each orbit only able to contain a set

number of electrons.


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Internal Structure of Atom

Atoms are made up of three

main particles:

Neutron, electron, and proton.

These main parts are each made

up of smaller particles .- Quarks, lepton


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Properties of the electron, proton, neutron

Particle Mass (g) SymbolMass(amu)

Charge(e)

Electron

Proton

Neutron

9.10939x10-28

1.67262x10-24

1.67493x10-24

e-

P

n

0.00055

1.00728

1.00866

-1

+1

0

Internal Structure of Atom

1 unit of mass is 1.661 x 10-27kg

Every atom has nearly all of its mass concentrated in the nucleus.


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The behaviour of protons, neutrons andelectrons in electric fields

What happens if a beam of each of these particles is passed between two

electrically charged plates - one positive and one negative? Opposites

will attract.

Protons are deflected on a curved path

towards the negative plate.

Electrons are deflected on a curved path

towards the positive plate.

Neutrons continue in a straight line.


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Proton Number and Nucleon NumberAn element (atom) is characterized by its:

Proton number (Z)

The number of protons in a nucleus

The atomic number of an element is what distinguishes it from all

other elements

Nucleon number (A)

Total number of protons and neutrons in a nucleus

nucleon number

protonnumber

XA

Z


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Determine the number of subatomicparticles in the following:

Cl has a nucleon number of 35 and proton number of 17

p+= 17, no= 18, e-= 17

Cl- = ?

K has a nucleon number of 39 and proton number of 19

p+= 19, no= 20 e-= 19

K+ = ?


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Isotopes

Isotopes have the same number of proton and electron but different number

of neutron.

Example : Hydrogen has 3 naturally occurring isotopes.


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Electron Arrangements Within Atoms

Electrons move rapidly in the space about an atomsnucleus.

The space is divided into subspaces called shells, subshells,

and orbitals.

SHELLS(n)

SUBSHELLS(l)

ORBITALS(ml)


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Electron Shells

Principal quantum number, n = 1,27

As the value of n increases:

- the energy increases

- the average distance of the electron from the

nucleus increases

Number of electrons in shell = 2n2

Shell 1 = 2(1)2= 2 electrons

Shell 2 = 2(2)2= 8

Shell 3 = 2(3)2= 18


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Electron SubshellsEnergy sublevels within energy level

All electrons in a subshell have the same energy

Designated s, p, d, f ..

Sublevel energy: s


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Electron Orbital Electron orbitals are regions within the atom whereelectrons have the highest probability of being found.

Each orbital can accommodate 2 electrons.

s subshell = 1 orbital

p subshell = 3 orbitals

d subshell = 5 orbitals


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s orbitals

1s 2s 3s


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Three p Orbitals


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Electron Configuration

List of subshells containing electrons

Written in order of increasing energy

Superscripts give the number of electrons

Example: Electron configuration of neon

number of electrons

1s2

2s2

2p6

main shell subshell


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Subshell Order

Subshell energy order (building-up order)

Based on mnemonic diagram

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


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Writing Electron Configurations

H 1s1

He 1s2

Li 1s2 2s1

C 1s2 2s2 2p2

S 1s2 2s2 2p6 3s2 3p4


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Electron configuration of TransitionElements

ELEMENT ELECTRONSCONFIGURATION

IN 4S AND 3D

ORBITALS

K 19 4s1

Ca 20 4s2

Sc 21 4s2 3d1Ti 22 4s2 3d2

V 23 4s2 3d3

Cr 24 4s1 3d5

Mn 25 4s2 3d5

Fe 26 4s2 3d6

Co 27 4s2 3d7

Ni 28 4s2 3d8

Cu 29 4s1 3d10

Z 30 4s2 3d10


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ELECTRONIC CONFIGURATION OF IONS

Positive ions (cations) are formed by removing electrons from atoms

Negative ions (anions) are formed by adding electrons to atoms

Electrons are removed first from the highest occupied orbitals (EXC.transition metals)

SODIUM Na 1s22s22p63s1 1 electron removed from the3s orbital

Na+ 1s22s22p6

CHLORINE Cl 1s22s22p63s2 3p5 1 electron added to the 3porbital

Cl 1s22s22p63s2 3p6


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FIRST ROW TRANSITION METALS

Despite being of lower energy and being filled first, electrons in the 4s orbitalare removed before any electrons in the 3d orbitals.

TITANIUM Ti 1s22s22p63s2 3p6 4s2 3d2

Ti+ 1s22s22p63s2 3p6 4s1 3d2

Ti2+ 1s22s22p63s2 3p6 3d2

Ti3+ 1s22s22p63s2 3p6 3d1

Ti4+ 1s22s22p63s2 3p6

ELECTRONIC CONFIGURATION OF IONS


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Sublevel Blocks


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Electron Configuration

Aufbau Principle:

orbitals fill in order of increasing energy from lowest

energy to highest energy

Pauli Exclusion Principle: only two electrons can occupy an orbital and their

spins must be paired

HundsRule:

when orbitals of equal energy are available but thereare not enough electrons to fill all of them, one

electron is added to each orbital before a second

electron is added to any one of them


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Orbital Diagram

CaAtomic number, Z = 20

Number of electrons = 20

Electron configuration (ground state):

1s2 2s2 2p6 3s2 3p6 4s2

Orbital diagram

1s 2s 2p 3s 3p 4s


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Ionisation Energy

The amount of energy required to completely remove anelectron from a gaseous atom.

Removing one electron makes a +1 ion.

The energy required is called the first ionization energy.

X(g) + energyX++ e-

Example:


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Factors Affecting Ionization Energy

1) The size of the nuclear charge

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2) Distance of outer electrons from the nucleus

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3) Shielding effect of inner electrons

The larger the nuclear charge, the greater the ionization energy.

The greater the distance between the nucleus and the outer

electrons of an atom, the less the ionization energy.

- The greater the shielding effect, the less the ionization energy.


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FirstIonization

energy

Atomic number

HeNe

Ar

Kr

H

Li

Na

K

Rb


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Ionization Energies (kJ/mol)

Element

Na

Mg

Al

Si

P

S

Cl

A

1st

498

736

577

787

1063

1000

1255

1519

2nd

4560

1445

1815

1575

1890

2260

2295

2665

3rd

6910

7730

2740

3220

2905

3375

3850

3945

4th

9540

10,600

11,600

4350

4950

4565

5160

5770

5th

13,400

13,600

15,000

16,100

6270

6950

6560

7320

6th

16,600

18,000

18,310

19,800

21,200

8490

9360

8780

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Chap 1 Atomic Structure

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