Bonding Flashcards by Emma Martin

What is electronegitivity?

The measure of the tendency of an atom to attract bonding pair of electrons in a covalent bond.

Greater the electronegitivity of an atom the more it attracts electrons towards it.

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Factors effecting electronegitivity

-atomic charge
-distance from nucleus
-electronsheilding

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Bonding between identical atoms (covalent)

They will be covalently bonded with 2 identical atoms the electrons are shared equally due to each atom having equal electronegitivity.

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Bonding between different atoms (covalent)

More electronegitive atom will have a greater share of electrons. The atoms therefore become slightly charged so it forms a polar covalent bond with a permanent dipole charge.

Symmetrical molecules are non polar despite containing polar bonds

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Patterns of electronegitivity

Across a period - increases due to increasing amount of protons

Down a group - decreases due to increased shielding and distance from the nucleus

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How does the size of electronegitivity affect type of bond formed?

Pure covalent = <0.4
Polar covalent = 0.4 - 1.8
Ionic = > 1.8

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Covalent bonds

-mostly occur between metals and non-metals which share electrons in outer shell to gain more stable ionic electron configuration.

One covalent bond = one pair of shared electrons

Held together via electrostatic forces of attraction between the nucleus of each atom and shared electrons

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Dative covalent bond

Where both electrons in the bond come from just one of the atoms involved. Represented by an aroow from electron donator.
Atom that accepts does not have a full outer shell so is electron deficient
Dative bonds do not differ in strength to regular covalent bonds.

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What is a lone pair?

When an electron is not used for bonding it is know as a lone pair

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Octet rule

Unpaired electrons pair up to obey the octet rule but this is not always possible as there may not be enough electrons avaliable.

Where 4 or more electrons pair up to bond it is called expansion of the octet and only occurs from period 3 and above due to more stable electrons

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Metallic bonding

Metals loose electrons to become ions and electrons are delocalised so metals form a lattice of positive ions surrounded by a sea of electrons.

-positive ions repel but is balanced via electrostatic attraction from electrons
-number of delocalised electrons depends on amount lost by each metal atom
-metallic bonding spreads throughout so metals have giant structures
-attraction is high so metals have high melting and boiling points
-metallic compounds are not soluble

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Why are metals good conductors of electricity?

Delocalised electrons more diectionally towards positive terminal inducing a current.

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Why are metals good conductors of heat?

They have high thermal conductivity as energy is spread via vibrations of closely packed particles and rapidly moving electrons

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Why do metals have high melting points?

Giant structure with large attraction so needs alot of energy to overcome

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What does the strength of a metal depend on?

The strength of the attraction controlled via:
-charge on ion (greater no. of electrons, stronger the attraction)
-size of ion ( electrons are closer to the positive nucleus in a small ion so stronger bond)

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Why are metals malleable and ducticle?

When metal is subjected to stress layer slide over eachother due to lattice causing manipulation. Will not occur in alloys.

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What is charge density?

Charge of ion/volume

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What is ionic bonding?

Occurs between a metal and a non-metal

-electrons are transferred from the metal with low electronegativity to non-metals with high electronegativity
-metals form cations and non-metals form anions
-ions are attracted to each other via electrostatic forces of attraction

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Properties on an ionic bond

-form ionic lattice due to non-directional bonding
-form cubic crystals due to the lattice structure
-high melting point due to large electrostatic forces of attraction
-conduct electricity when molten as ions are free to move

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Covalent Bonding

Mostly occurs between metals and non-metal

-sharing of electrons in the outer shell so each atoms has a stable configuration
-atoms remain neutral
-forces of electrostatic attraction occur between the nucleus of each atom and shared electrons

Dative Covalent Bonding

-where both electrons in the covalent bond comes from one atom
-represented by an arrow from electron donor
-atom that accepts is electron deficient
-same strength and length as normal covalent bonds

Properties of covalent bonds

-low melting points as there is weak attraction between molecules
-poor conductors due to no free charged particles
-dissolve in water and remain as molecules

3 types of intermolecular forces

-van der val
- dipole dipole
-hydrogen

Van der val forces

-distribution of electrons in an atom will cause attractions between other atoms and temporary poles will become induced
-occur in all molecules at all times
-size increases as number of electrons increase
-high boiling point of noble gases and boiling point of hydrocarbons is explained by this
-they are easily broken and reformed

Dipole Dipole forces

-occurs between molecules with permanent dipoles (polar covalent) -attractions are not permanent and have enough energy to be overcome

Hydrogen bonding

-form between molecules that have N-H, O-H or F-H bonds -must be a hydrogen atom that is boned to a very electronegative atom causing hydrogen to form slight positive charge -another very electronegative atom with lone pair of electrons will be attracted to the H+ forming a bond

Heating solids

Heating a solid will supply energy to the particles causing more vibrations which will lead to increasing distance causing the solid to expand

Solid to Liquid

-energy needed to weaken forces between molecules enthalpy change of melting -temperature does not change as heat energy is absorbed as forces weaken

Heating a liquid

-supply energy to particles to make them move quicker. liquids also expand

Liquid to gas

-break all intermolecular forces enthalpy change of vapourisation no tempreture change

Heating a gas

gain kinetic energy and move faster to expand

What are crystals?

solids that have a regular arrangement that are held together via attraction of forces. The strength of the forces determines the physical properties of the crystal

Ionic Crystals

-strong electrostatic forces of attraction so have high melting point -cannot conduct electricity as ions are fixed as a solid

Metallic Crystals

-lattice of positive ions with sea of delocalised electrons -high melting point -conduct electricity and heat -ductile

Molecular Crystals

-consist of molecules held together via intermolecular forces (covalent bonds within molecules) -low melting points due to weak intermolecular forces -soft -does not conduct electricity

Macromolecule crystals

-covalent bonds extend throughout structure and cause giant structure with strong bonds so has high melting points

Diamonds

-carbon forms 4 bonds forming giant structure -bond angle 109.5 -tetrahedron -hard -high melting point >3700 K -does not conduct electricity

Graphite

-carbon forms 3 bonds -bonding angle 120 -trigonal planar -strong covalent with weaker van der vals between layers -layers held via van der vals so they slide over each other -high melting point -soft -conducts electricity due to delocalised electron from p orbitals which flow along planes.

Giant footballs

forms of carbon known as nanotubes or buckyballs that can be used in sports equipment or for medical treatments

Electron Pair Repulsion

-each pair of electrons around an atom will repel all other electron pairs -pairs of electrons will take up space as far apart as possible to minimise repulsion -pairs may be shared or lone

What does the shape of a molecule depend on?

-number of pairs of electrons around the central atom -lone pairs; as for every lone pair bonding angles are reduced by 2 degrees as they repel -a square planar is formed when a octahedron contains 2 lone pairs as they repel

Shapes of molecules

2 pairs - linear 180 3 - trigonal planar 120 4- tetrahedron 109.5 5- trigonal bipyramid 6- octahedral 90

Repulsion scale

Repulsion will increase bonding pair - bonding pair lone pair - bonding pair lone pair - lone pair

VSESPR theory

1) identify central atom 2) count number of outer shell electrons 3) add 1 electron for each bonding atom 4) add/subtract electrons for any charges 5) divide total by 2 to find total number of electron pairs 6) work out bonding and lone pairs (how many bonds are formed) 7) use numbers to predict a shape

Explain in terms of intermolecular forces present why HF has a higher boiling point than HCl.

-HF contains hydrogen bonding of which is occurring between the H and F -HCL only contains slight dipole dipole charges and vdws -these are weaker and therefore require less energy to be broken

Predict the shape of an AlH4- ion and explain why it has that shape

-tetrahedral shape -equal repulsion between the 4 bonding pairs that surround Al

Suggest why graphite has a very high melting and boiling point

-have very strong covalent bonds -macromolecular

Explain the movement of atoms in a crystalline solid

vibrate about a fixed position