Atomic structure

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Physical chem year 1

by Jorja S.

Whats the atomic number?

What's the mass number?

How many protons does it have?

How many neutrons does it have?

Relative charge of a proton

Relative charge of a neutron

Relative mass of a proton

Relative mass of a neutron

Relative mass of an electron

Atomic number =

Number of protons

Mass number =

Total number of protons and neutrons

Number of neutrons =

Mass - Atomic

What does a positive charge mean?

Number of lost electrons

What does a negative charge mean?

Number of extra electrons

Relative charge of an electron

-1

How many electrons does it have?

What does the charge mean?

It's gained 3 electrons

What is this called?

Nuclear symbol

How are electrons arranged?

In electron shells

Shells have …

Sub shells

What's each sub-shell made up of?

Electron orbitals which can hold 2 electrons which spin in opposite directions

What are orbitals?

Regions of space that electrons are most likely to be in

What does electron configuration determine?

Reactivity

What's Aufballs principle?

Electrons enter the lowest energy orbital available

What's Hunds rule?

Electrons prefer to occupy orbitals on their own and only pair up when no empty orbitals of the same energy are available

What's the order of filling orbitals?

1s² 2s² 2p⁶ 3s² 3p³ 4s² 3d¹⁰ 4p⁶

Are electrons lost from 4s or 3d first?

Why are orbitals filled in numerical order?

Because principle energy levels get closer together as you get further from the nucleus

What did Bohr state about the atom?

Small nucleus of protons and neutrons surrounded by circulating electrons

Each shell/energy level could hold max number of electrons

Energy of levels become greater as for further from nucleus

Electrons filled energy levels in order

1st shell = 2

2nd shell = 8

3rd shell= 18

4th shell = 32

5th shell= 50

What happens to the electron configuration when ions are formed?

Highest energy electrons are most first

When simplifying e.c, what do you look at?

Nobel gases

What are the exceptions to the configuration re regarding 4s orbital?

Chromium

Copper

What changes in the electron configuration with chromium and copper?

4s orbital still filled before 3d but only occupied by 1 electron

Give the configuration of chromium

1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d⁵

Give the configuration of copper

1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d¹⁰

What factors affect I.E?

Nuclear charge

Distance from nucleus

Shielding

How does nuclear charge affect I.E?

The more protons in the nucleus, the higher the positive charge, so the stronger the attraction for the electrons

How does distance from nucleus affect I.E?

Attraction decreases with distance. An e- closer to the nucleus will be more strongly attracted that ones further away

How does shielding affect I.E?

An electron in an outer shell is repelled by electrons in complete inner shells, weakening the attraction to the nucleus

What's an isoelectronic ion?

Charged particle which has same number of electrons

How's the period table arranged?

By atomic number

Elements in same period …

Have same number of shells

Elements in same group…

Have same number of electrons in the outer shell so similar properties

What's the periodic table split into and why?

4 blocks to show which subshell outermost electron of element is in.

E.g 1s² 2s² 2p⁶ - in p block

What's ionisation energy?

Measure of the amount of energy needed to remove electrons from atoms

Why's there a great attraction between protons and electrons?

Electrons -vely charged and protons +vely charged

The greater the pull of the nucleus…

The harder it will be to pull an electron away from an atom

What's the first ionisation energy?

Energy needed to remove one mole of electrons from one mole of atoms in the gaseous state

1st I.E =

Remove 1st electron

2nd I.E =

Remove 2nd electron (not 2 electrons)

General equation for I.e

Why do neutral atoms and molecules need to be ionised?

To accelerate them

To deflect them to the negative plate

What are the 2 ways of ionising samples?

Electron impact ionisation

Electrospray ionisation

What are the stages of time-of-flight mass spectrometry?

Ionisation

Acceleration

Flight tube

Detection

What's a time-of-flight mass spectrometer used for?

Measuring the masses of atoms and molecules

Measure the relative abundance of different isotopes

To predict the structure of more complex molecules

What happens during electron impact ionisation?

Sample is bombarded with high energy electrons from electrongun. Knocks an electron off the atom/molecule to form a positive ion. The Ar/Mr of ion will be the same as the m/z recorded on the spectrum

What happens during electrospray ionization?

The sample is dissolved in a volatile solvent than injected through a needle at high today causing molecule to gain a proton (M + H+ →MH+)

Mr of molecule will be one less than me m/z value due to the added proton

What happens during acceleration?

Positive ions are accelerated using an electric field

All ions have same kinetic energy when accelerated by the electric field

KE =

½mv²

√(2KE/m)

KE = ½mv²

KE in

m in

V in

Joules (J)

ms-¹

What happens in the flight tube?

Lighter particles move faster so have shorter time of flight

t =

d/v

t=d/v

t in

d in

Seconds

Meters

What happens during detection?

Positive ions hit a negatively charged electric plate

When hit plate, the positive ions are discharged by gaining electrons from the plate. This generates a movement of e-s and an electric current that can be measured

Size of current is relative to abundance of each isotope

What is relative atomic mass?

The average mass of an atom of an element compared to 1/12 the mass of an atom of carbon-12

How can relative atomic mass be measured?

Using time-of-flight mass spectrometer

What are isotopes?

Atoms with the same number of protons and electrons but different number of neutrons

Isotopes have the same …. number but different …

Atomic

Mass number

Isotopes have the same … why?

Chemical properties as have same electron configuration

Isotopes have slightly different … why?

Physical properties as this depends on mass

R.A.M =

Definition of relative atomic mass

The average mass of an atom of an element compared to 1/12 the mass of an atom of carbon-12

When does ionisation energy increase?

Down a group and across a period

Why does ionisation energy increase down a group?

Outer electron further away from nucleus so weaker attraction between nucleus and outer electron

Outer electrons are in higher energy orbitals and so have more shielding weakening the attraction

Why is there a general increase in ionisation energy across a period?

Increasing number of protons so greater attraction between nucleus and outer electron

Electrons added to same shell so same shielding across period

Describe the trends in ionisation energy in period 3

General increase

Drop between group 2 (Mg) and group 3 (Al)

Drop between group 5 (P) in group 6 (S)

Why is there a drop in ionisation energy between magnesium and aluminium?

Outer electron in aluminium is in 3 p subshell

3p is higher in energy than 3s so weak attraction than in Mg

Why is there a drop in ionisation energy between phosphorus and sulphur?

Outer electron begins to pair in 3 p orbital in sulphur increasing electron repulsion, paired electrons repel

Is the first or second ionisation energy larger?

Second

Why is the second ionisation energy always larger than the first?

Takes more energy to remove an electron from a positive ion

When is there a large increase in ionisation energy?

When there's a change in shell (decrease in shielding)