Chemistry- Unit 1- Bonding

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  • Created by: FireDwarf
  • Created on: 27-10-13 15:04
why do chemical bonds form?
So that atoms can become stable and therefore gain electronic configuaration to their closest noble gas
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ionic bonding?
Metals and Non-metals, Metals lose and non-metals gain, these form positive and negative ions which attract to each other.via electrostatic charge
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What is ionic bonding a result of?
Electrostatic attraction between oppositly charged ions
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Shape?
Lattic- result of the opposete charges being attracted and the same repelling each other.
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Lattice?
co-ordination number- number of joins the ion makes with the opoosetly charged ion (count from center)
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Properties?
Giant structures- high melting point and boiling point- Lattice of ions is strong (electrostatic). Conduct electcity when molten or aqueous, due to electrons being set free, Brittle, due to if given sharp blow, the same charges of ions may be close
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conc
to each other therefore causing a repulsion therefore making it easier to split.
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What is a covalent bond?
Bond between two non-metals, atoms share electrons. A convalent bond is a bond where 2 electrons are shared between two non-metals.
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why?
To become stable by forming the closest noble gas electronic configuaration
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How are they held together?
By the electrostatic attaction between the nuclei and the shared electrons.
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Double convalent bond?
Four electrons shared.
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Properties?
Low melting points, weak attraction van der walls between molecules, easilly broken up.
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conc
Poor conductors because their molecules are neutral overall, no charged particals.
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Co-ordinate bonding? Dative?
When one atom shares both the electrons (lone pair) and the other none (electron defficant)
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Example?
Ammonia atom (NH4+)
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Electronegativity?
Power of an atom to attract the electron density in a convalent bond to itsself.
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what is it dependant on?
Nuclear charge, the distance between the nuclues and outer-shell electrons, shielding of inner electrons
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Trends?
Up the periodic table, increases, across the periods, increases. F,O,N therefore most electronegativity.
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Polarity?
Unequal sharing of electrons between atoms bonded convalently.
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The same electronegativity?
There is no polarity (non-polar) as the electrons are distributed equally.
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Diffrent?
Electrons may be pulled towards one of the atoms more, resulting in a polar convalent bond.
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What are the three types of inter-molecular forces?
Van der Waals, dipole dipole and hydrogen bondng. (weak to strong)
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What are Van der Waals?
electrons are constantly moving, giving instantanious dipoles. These dipoles then induce a dipole in the other atoms, therefore causing tempoary dipoles to form. This causes instantanious forces of attraction.
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How do van der waals become stronger?
More electrons & increase in molecular size (eg: s8 compared to p4)
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Why are they weak?
Because they are contantly being made and broken as the instantanious diploe induced dipolar forces are only there for a short amount of time, then get broken, so not much energy is needed to break them.
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Dipole-dipole forces?
Due to permament dipoles which are formed due to electronegitvity. Due to an uneven ratio of electrons between the molecule, there is a slight + and slight - atom, causing attraction therefore.
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What is hydrogen bonding?
Hydrogen bonding is a hydrogen atom gets sandwitched between two electronegative atoms.
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What are the conditions needed for it to occur?
Very electronegative atom & a lone pair of electrons convalently bonded to the hydrogen.
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What occurs?
The hydrogen atom will become + because it is bonded to a very electronegative atom (therefore causing a strong + charge on the H). The lone pair will then be attracted to the hydrogen atom
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Therefore what are the only atoms that are electronegative enough?
O,F,N
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Boling points?
Hydrogen bonding is the strongest inter-molecular force. Therefore more energy is required to break molecules up which have these forces between them. Therefore, they have higher boiling points.
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Importance of H bonding?
They are good for a variety of reasons as they are stronger then van der walls and dipole-dipole, but can be easier broken then convalent or ionic.
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Example?
Ice- water molecules are connstantly moving therefore hyodgen bonds are being broken and made easilly. When frozen, hydrogen bonds hold molecules in fixed state, forming a structure simular to diamond. Molecules less packed in, less dense then water
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DNA?
Hydrogen bonds are formed in the secondary structure netween the NH and C=O bonds. These form alpha helixs and beta sheets. Break hyoden bonds, change in shape, denatured.
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Irons?
Breaks hydrogen bonds in the crumpled clothing, causes the molecules to be pressured into forming new posistons, so the shape becomes flat.
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DNA?
2 strands of the spiral are held via hydrogen bonds. When the cell divdies, the H bonds break,
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How does metallic bonding occur?
Outer shell of electrons are delocalised and able to move. This forms the sea of electrons. Positive ions now attracted to these free, delocalised electrons.
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What makes metallic bonding stronger?
Higher charge density- more free electrons (therefore higher group) within the area & giant structures
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Metals properties
Good conductors, free electrons which are able to carry the current. As an electron joins in the negative terminal as an electron leaves at the postive terminal. They conduct heat, energy spread by the vibrations of the closlypacked ions
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Strengh?
Dependant on the charge and size of the ion. They are storng generally because the electrons are free and therefore theses no individual bonds to break.
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Malleable and ductile?
Beaten into shape & pulled into thin wires. This is because the ions are bound by the electrons and remain in the exact same envrioment, so shape is retained.
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What ias electron replusion theory?
Each pair of electrons wull repel all other pairs and therefore will want to be the furthest away from each other as they can.
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What can electron pairs be?
A shared pair & lone pairs. (shared in a convalent bond, lone without a bond)
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Two pairs?
Linear, 180, BeCl2
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3?
Trigonal planar, 120, alcl3
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4?
Tetrahedal, 109.5, ch2
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5?
Trigonal bipyramid, 90 & 120, PCL5
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6?
Octahedral, 90, SF6
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What ooccurs if theirs lone pairs?
They can effect the shape because they have greater repulsion and can cause bonds to be pushed together.
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Example?
NH3, 4 pairs of electrons & 1 is a lone pair. 4 normally is a tetrahedal however the bonds are distorted and the angle changed into a triangular pyramidal.
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Water?
Forms a V shaped
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Clf4 (4 bonds)
square planar
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Heating a solid? What occurs?
Supply energy which causes the particals to vibrate more on their fixed posistion, which causes them to move further apart and therefore the solid expands.
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Heating a solid into liquid? What occurs?
Called fusion, supply more energy, weaken the forces between the particals.
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What is the energy supplied called?
enthalpy change of fusion
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What is enthalpy?
Heated measured under constant pressure.
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Why does the temperture of the solid not change when heated?
Because the particals are absorbing the energy.
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heating liquid?
Supply energy to the particals, they move quicker and therefore move further apart.
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Liquid to gas?
Called vapourisation- Break all intermolecular forces. Enthapy change of vapourisation. No temp change agian.
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heat gas?
More kinetic energy- particals move even further apart- expand.
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Crystals? Ionic?Metallic?
Soilds, diffrent types depedant on forces attracting. Ionic- strong attraction between opposite charged ions. Mettallic- + ions with sea of electrons
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Molecular? Macromolecular?
Van der waals hold it in a solid shape. Macro- convalent bonds extend through the compound and are simular to giant strructures.
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What is diamond?
Diamond- pure carbon colvalent bonds- 4 convalent bonds formed per carbon. Forms a tetralhedral shape with 109.5 degree angles. Hard material,high temp due to convalent bonds, no conducting.
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Graphite?
Pure carbon, 3 convalent bonds formed (traingolar planar 120). Each carbon has a spare delocalised electron which allows for conducting. Low melting temp, conducts and soft material.
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ionic bonding?

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Metals and Non-metals, Metals lose and non-metals gain, these form positive and negative ions which attract to each other.via electrostatic charge

Card 3

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Card 4

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Shape?

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Card 5

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Lattice?

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