Chemistry - Topic 2

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Actions of Atoms-->Ions
Metals lose electrons to form cations, non-metals gain electrons to form anions. Do this to gain electron configuration of the nearest noble gas
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Ionic Compounds
Ions arrange in a giant ionic lattice. Held together by strong electrostatic forces of attraction. Bond strength affected by charge and radii
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Properties of Ionic Compounds
hard, brittle, high melting+boiling points, soluble in polar solvents, conduct in solution
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Define Covalent Bonding
the electrostatic forces of attraction between +vely charged nuclei and the pair of electrons that they share
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Covalent bonds can form between....
(1) atoms of the same element (2) non-metals (3) one element in Group 4 (4) top-of-the-group elements
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Define Lone Pair
a pair of electrons in the outer shell of an atom involved in a covalent bond
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Define Dative Covalent Bond
a covalent bond formed when one atom supplies both electrons that are shared, the other atom accepts both into a vacant orbital
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Bond length + Bond strength
depends on the size of atoms + the number of electron pairs. Larger atoms form longer bonds as they have more electrons that shield the nuclei and reduce attraction. Single bonds are longer than triple bonds. strength varied inversely to length
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Simple Molecular Structures (intra+intermolecular forces)
Intramolecular forces are strong (covalent). Intermolecular forces are weak.
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Properties of Simple Molecular Structures
gases/liquids/soft solids at room temp. low mp + bp. do not conduct. soluble in non-polar solvents.
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The Expansion of the Octet
Phosphorous has 3p3, and has 3 unpaired electrons that want to form 3 covalent bonds. It also has 5 empty 3d orbitals, and a full 3s orbital. It moves an electron from the 3s to the 3d, forming 5 unpaired electrons.
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Define Bond Angle
the angle between 2 covalent bonds in a molecule or giant covalent structure.
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Define isoelectronic molecules
molecules and ions that have exactly the same number + arrangement of electrons
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lone-lone , lone-bonding , bonding-bonding - strength of repelling effect
lone-lone > lone-bonding > bonding-bonding
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Define Electronegativity
the ability of an atom to attract the bonding electrons in a covalent bond. in a polar bond, the shared electrons are pulled towards the more electronegative atom
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Electronegativity 1
If the 2 atoms in a covalent bond are the same, the bond is purely covalent. If the two atoms are different, the pair of electrons are not shared equally. The nucleus of one atom attracts the electrons more strongly than the other.
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Define polar covalent bond
bonds between atoms of different elements. the shared electrons are pulled towards the atoms with the strongest pull. has a dipole.
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Electronegativity (EN) 2
In this case, one end of the bond is slightly -ve, and vice versa. It is a polar covalent bond.
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Electronegativity trends
EN increases going across a period as the nuclear charge increases, shielding is constant, so attraction increases. EN decreases going down a group as despite nuclear charge increasing, there is an increase in shielding.
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The Pauling Scale
Goes from 0 to 4. Increases along a period and across a group. compare electronegativity quantitively.
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Factors affecting EN
(1) shielding (2) atomic radii (3) nuclear charge
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Define Polar Molecules
molecules that contain polar bonds which do not cancel each other out, so the whole molecule is polar
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Polar Molecules
Little electrical dipoles (2 oppositely charged ends). they line up in an electric field. The bigger the dipole, the bigger the twisting effect.
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Define Intermolecular forces
weak attractive forces between molecules.
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Define Intramolecular forces
relatively strong covalent bonds linking the atoms in molecules
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Define London forces
the intermolecular forces that exist between all molecules. they arise from the attractions between temporary instantaneous dipoles and the fleeting dipoles they induce in nearby molecules
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London Forces
when non-polar atoms/molecules meet, there are fleeting repulsions and attractions between the nuclei and the surrounding clouds of electrons. temporary displacements of the electrons lead to temporary dipoles. +ve poles induce -ve poles.
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Define polarisability
an indication of the extent to which the electron cloud in a molecule can be distorted by a nearby electric charge.
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London forces in larger molecules
Bigger molecules with a larger no of electrons have a higher polarisability, and the possibility for temporary induced dipoles is greater.
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The effect of the shape of a molecule on London forces
The attractions between long thin molecules are stronger than those in short fat molecules. due to a larger surface area. the more branched a molecule is, the more spherical and compact it is, so branched alkanes have weaker IM forces
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Dipole-Dipole Interactions
Molecules with permanent dipoles attract each other more strongly. +ve attracts -ve. This acts in addition to London forces.
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Hydrogen Bonding
Affects molecules where hydrogen is covalently bonded to a highly electronegative element (F, N or O). The -ve atom attracts the electron strongly away from the H, so H is very +ve. H+ attracts lone pair on -ve element on another molecule.
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Define Hydrogen Bonding
a strong intermolecular force between a +ve hydrogen atom covalently bonded to F,N or O and a lone pair of electrons on the -ve F,N or O on a nearby molecule.
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Define solubility
a measure of the concentration of a saturated solution of a solute at a specified temperature
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Solubility+Intermolecular Forces
Solubility patterns depend on intermolecular forces between (1) solute molecules (2) solvent molecules (3) solute and solvent molecules . When all 3 are the same strength, the solute dissolves freely in the solvent.
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Solubility in Non-Polar molecules
They do not dissolve in water. the non-polar molecules can separate due to weaker intermolecular forces. H bonds in water act as barrier that keeps out molecules unable to form H bonds themselves
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Solubility of Polar Organic Molecules
Also insoluble in water. Weak dipole-dipole forces between molecules allow them to separate easily. but can't form H bonds with water
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Solubility of Organic molecules
Soluble in water as they can form H bonds so dissolve and mix with water.
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Solutions of Ionic Salts in Water
To be soluble, ions are strongly HYDRATED by water. they cluster around the ions and bind to them. the energy released when the water molecules bind is enough to compensate for the energy needed to overcome the electrostatic attract
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Why are some ionic salts soluble and some not?
In insoluble salts, the hydration energy that would be released when ions are hydrated is not enough to overcome the forces of attraction in the lattice
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Define Hydration
takes place when water molecules bond to ions or add to molecules. polar water molecules are attracted to +ve and -ve ions
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Properties of Giant Covalent Structures
hard, high melting+boiling points
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Define Allotropes
different forms of the same element in the same physical state
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Each carbon atom bonded to nearest 4. Tetrahedral structure. Doesn't conduct electricity as no free electrons. Conducts thermal energy. Cutting+jewellery
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Arranged in hexagons, each carbon bonded to the nearest 3. Trigonal planar structure. 4th free electron joins sea of delocalised electrons so graphite conducts electricity. H bonds between layers. Soft and greasy
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A molecular form of carbon. Black solids, soluble. Same bonding as carbon. Grp1+2 metals react to form superconducting systems that conduct at low temps.
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A single layer of graphite. Thin but very strong. Conducts electricity
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Define Delocalised Electrons
bonding electrons that are not fixed in a bond between 2 atoms, free to move and shared by many atoms
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Define metallic bonding
the strong electrostatic attraction between metal ions and the sea of delocalised electrons
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Properties of Metals
high mp+bps. high densities. good conductors of heat and electricity. malleable as bonds are strong but not directional
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Card 2


Ionic Compounds


Ions arrange in a giant ionic lattice. Held together by strong electrostatic forces of attraction. Bond strength affected by charge and radii

Card 3


Properties of Ionic Compounds


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Card 4


Define Covalent Bonding


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Card 5


Covalent bonds can form between....


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