notes for OCR Unit 1, Module 2: Electrons, Bonding and Structure

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Preview of notes for OCR Unit 1, Module 2: Electrons, Bonding and Structure

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Anusha S. UNIT 1; MODULE 2: ELECTRONS , BONDING & STRUCTURE
1.2.1 EVIDENCE FOR SHELLS
Ionisation energy
1st ionisation energy is energy required to remove one electron from each atom of a gaseous mole
of atoms to produce one 1 mol of gaseous 1+ ions.
Requires less energy than next IE and is a measure to see how easily an atom loses an e-
Provides model of atom where there is a nucleus and electrons is shells
Factors affecting ionisation energy
Electrons held in shells by attraction to positive nucleus.
To form positive ion, energy supplied to e- to overcome attraction to nucleus. 1st e- is easiest to get
off from the atom. Successive IEs' are stronger.
The nuclear attraction is dependent on 3 factors...
1) Atomic radius; the greater the atomic radius, the smaller the nuclear attraction on outer e-
2) Nuclear charge; the greater the nuclear charge, the greater the attractive force on the outer e-
3) E- shielding; inner shells repel outer shell e- so the more inner shells, the smaller the nuclear
attraction experienced by outer e-
Successive IEs
This is the measure of energy required to remove each e- after the first e-.
An element has as many IE's as e- on atom
Each successively increases as there is less repulsion by electrons and nuclear attraction is stronger
and each shell is more drawn to the nucleus.
When the e- is taken from next shell, the IE is much lower, significantly
1.2.2 SHELLS AN D ORBITALS
Energy levels
Successive IE provides evidence for; presence of shells and no of e- in each shell
A shell is a group of orbitals w/ same quantum number `n'
Atomic orbitals
It's a region w/in an atom that can hold up to 2e- w/ opposite spins.
Each shell is made up of atomic orbitals
4 types of orbitals; s, p, d &f
Orbitals hold 2 e- w/ opposite spins
Electrons have duality of nature meaning they act like a wave and particle at the same time. We
never know the exact location of e- but we can predict it and we know that it is in the orbital.
This helps chemists when describing behaviour of atoms and how elements react but also
structure of Periodic Table
1 Electrons, bonding and structure (Anusha S.)

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Anusha S. UNIT 1; MODULE 2: ELECTRONS , BONDING & STRUCTURE
1.2.3 SUB-SHELLS AND ENERGY LEVELS
Sub-shells
Is a group of the same type of atomic orbitals w/in a shell
An e- shell is made w/ same q p no `n'.…read more

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Anusha S. UNIT 1; MODULE 2: ELECTRONS , BONDING & STRUCTURE
Chemical Bonding
It's classified into 3 main types; covalent, ionic and metallic.
A compound formed when atoms of dif elements are in same proportions
Ionic bonding
Occurs in metal and non-metal compounds
If imagined bond formed between atoms, e- is transferred from metal non metal
Forms oppositely charged ions that attract
Covalent Bonding
Is in compounds of 2 non-metals where the e- s shared between the atoms (e.g.…read more

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Anusha S. UNIT 1; MODULE 2: ELECTRONS , BONDING & STRUCTURE
1.2.7 IONS & THE PERIODIC TABLE
Predicting ionic charges
Can predict charges on ion from element in PT
Can find out elements e- so can calculate how many needed to drop or gain to reach noble gas e.c.…read more

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Anusha S. UNIT 1; MODULE 2: ELECTRONS , BONDING & STRUCTURE
1.2.9 FURTHER COVALENT BONDING
Dative covalent bonding
Is when the covalent bond is formed by one atom donating both electrons in the bond to the other atom.…read more

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Anusha S. UNIT 1; MODULE 2: ELECTRONS , BONDING & STRUCTURE
Molecules with lone pairs
Lone e- pairs are slightly more e--dense that bonded pair where
relative strength of repulsion =
· Lone pair| Lone pair < lone pair| bonded atom < bonded pair| bonded
pair.
Each lone pair reduces bond angle by 2.5o so there is extra
repulsive effect of each lone pair
Molecules with Double bonds
Double bonds have 4 e- as there are 2 bonded pairs.…read more

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Anusha S. UNIT 1; MODULE 2: ELECTRONS , BONDING & STRUCTURE
Electronegativity & bonding type
Bonding between atoms of two different elements with a small difference in electronegativity. The
more en atom will have a little bit more of a share of the e-s which gives a polar covalent bond.
Bonds with a large difference in en between the 2 atoms of different elements more en atom
effectively takes both e- = gives an ionic bond.…read more

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Anusha S. UNIT 1; MODULE 2: ELECTRONS , BONDING & STRUCTURE
Van der Waals' forces increase as e- increases. The greater no. of e-, the larger the induced dipoles,
the greater the attractive forces between molecules, which are the van der Waals' forces.
Boiling points and van der Waals' forces
Van der Waals' forces are only attractive intermolecular forces acting between non-polar
molecules.
As no.…read more

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Anusha S. UNIT 1; MODULE 2: ELECTRONS , BONDING & STRUCTURE
Special properties of water
H-bond in H2O has strength enough to affect properties in unexpected ways:
1. Ice is less dense than water as it has an open lattice with h-bonds holding H2O
molecules apart whereas when melted, the H-bonds collapse and the H2O moves closer
together so, ice is less dense.
2. It has a relatively high b.p and m.p due to strong H-bonds between H2O molecules.…read more

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Anusha S. UNIT 1; MODULE 2: ELECTRONS , BONDING & STRUCTURE
Properties of giant metallic lattices
· Most metals have high melting and boiling points as the attraction between the fixed
positive ions and the free, delocalised e- are very strong. This means that a high amount of
energy is needed to break the metallic bonds and dislodge ions from fixed position in lattice.
· Good electrical conductivity as there are free-moving delocalised e- that can move freely
w/in the metallic lattice.…read more

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lovebiology101

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