Electrons bonding and Structure

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Define 'First Ionization Energy' of an element.
The energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous atoms to form one mole of gaseous 1+ ions.
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How does atomic radius affect ionisation energy?
The greater the atomic radius, the smaller the nuclear attraction experienced by the outer electrons, the smaller the ionisation energy.
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How does nuclear charge affect ionisation energy?
The greater the nuclear charge, the greater the attractive force on the outer electrons, the larger the ionisation energy.
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How does electron shielding affect ionisation energy?
The more inner shells there are, the larger the shielding effect and the smaller the nuclear attraction experienced by the outer electrons, therefore the smaller the ion
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How many electrons can occupy the third shell?
18 electrons
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How many electrons can occupy the fourth shell?
32
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Define 'Principal Quantum Number'
The principal quantum number indicates the shell that the electrons are in.
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Why is a Magnesium atom smaller than a Sodium atom?
Mg and Na have the same number of electron shells, however Mg has one more proton than Na and so has a stronger positive nuclear pull on the outermost electrons; this means electrons will be pulled in further than those in Na, reducing the atomic rad
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What is the bond angle of an Octahedral shaped molecule?
90 degrees
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The maximun number of electrons that can pair up is equal to...
...the number of electrons in the outer shell.
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Give an example of the expansion of the octet rule and explain why it works.
Sulfur hexafluoride, SF6 : This compound has more than 8 electrons in its outer shell and sulfur can form 6 covalent bonds with fluorine, which has 7 electrons in its outer shell, this results in sulfur having 12 electrons in its outer shell in SF6.
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What is the octet rule?
When covalent bonds form the unpaired electrons pair up so that the bonded atoms obtain a noble gas config, with 8 electrons in the outer shell.
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Why does the octet rule not always work?
There may not be enough electrons to react an octet. More than four electrons may pair up when bonding occurs.
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Why do molecules with more lone pairs have smaller angles?
A lone pair is more repulsive than a bonding pair, therefore lone pairs will push bonded electron pairs close together to decrease the angle.
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Double bonds are counted as single bonding regions, knowing this, what is the bond angle and shape of Carbon Dioxide, which has 2 double bonds.
Carbon dioxide will be linear and have a bond angle of 180 as it has 2 bonding regions and no lone pairs.
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What is a dative covalent bond?
A shared pair of electrons which has been provided by one of the bonding atoms only.
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Define electronegativity.
A measure of the attraction of a bonded atom for the pair of electrons in a covalent bond.
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What is a permanent dipole?
A small charge difference across a bond that results from a difference in the electronegativities of the bonded atoms.
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What is the trend of electronegativity across a period and down a group.
Electronegativity increases along a period and decreases down a group.
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Explain why a H-Cl bond is polarised.
Cl is more electronegative than than H, bonding electrons are attracted more by the Cl atoms and so the electrons are slightly more distributed around the Cl atom. This created a dipole ( a small charge difference ), therefore the bond is polar.
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Why is C-Cl4 not a polar molecule?
All the dipoles cancel out as the molecule is symmetrical.
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Why is a H-H molecule non-polar?
Both hydrogen atoms are equally electronegative therefore electrons in the bond are evenly distributed.
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Why is NaCl an ionic bond ( in terms of electronegativity ) ?
There is a large difference in electronegativities between Na and Cl, therefore the more electronegative bonding atom will complete capture both bonding electrons.
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What is the shape and bond angle of an Ammonium ion? Explain why.
An ammonium ion has a tetrahedral shape and a bond angle of 109.5. This is because it has 4 bonding pairs of electrons and no lone pairs, therefore all the bond angles are 109.5 as charge clouds will repel eachother equally.
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What is the shape and bond angle of a molecule with 2 bonding pairs and 3 lone pairs?
Linear shape, 180
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What is the shape and bond angle of BeCl2? Explain why.
Beryllium chloride has a linear shape and a bond angle of 180 as it has 2 bonding pairs of electrons and 0 lone pairs.
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What is the bond angle of a trigonal bipyramidal shaped molecule? Why?
Bond angle is either 90 or 120, bcause it has 5 bonding pairs and 0 lone pairs.
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What is the bond angle of a trigonal planar shaped molecule? Give an example and state why.
The bond angle is 120, for example, in BF3, this is because the molecule has 3 bonding pairs and 0 lone pairs.
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Describe a pyramidal shape molecule.
A pyramidal molecule has 3 bonding pairs of electrons and 1 lone pair of electrons. It has bond angle of 107.
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Explain why the bond angle in a trigonal pyramidal shape is smaller than that in a trigonal planar.
A triganol planar molecule hasno lone pairs, so the bond angles are all equal. In a pyramidal there is a lone pair (more repulsive than bonding pairs) pushing the bonded pairs closer together - creates a smaller angle.
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What is the shape of a molecule with either 2 bonding pairs and 2 lone pairs, or 2 bonding pairs and 1 lone pair? What is the bond angle?
Bent/angular/non-linear. The bond angle is 104.5.
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Give an example of a non-linear molecule.
Water
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What is a hydrogen bond?
A strong dipole-dipole attraction between an electron deficient H atom on a molecule and a lone pair of electrons on a highly electronegative atom
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What are van der waals forces?
The weakest intermolecular force, caused by temporary dipoles, which causes all atoms and molecules to be attracted to eachother
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How do van der waals forces arise?
The movement of electrons in shells cause instantaneous temporary dipoles, these dipoles induce further dipoles between neighbouring molecules. All these small induced dipoles attract each other to create weak intermolecular forces (van der waals ).
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Why do boiling points increase as you go down the noble gas group (in terms of van der waals forces)
The number of electrons increase, therefore the van der waals forces increase, this means there are stronger intermolecular forces that require a larger amount of energy to be overcome, therefore the boiling point will increase.
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Explain why ice is less dense than water.
Ice is an open lattice where water molecules are held apart by hydrogen bonds. When ice melts the rigid hydrogen bonds collapse allowing water molecules to move closer together therefore water is more dense than ice.
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Explain why water has a relatively high melting and boiling point.
Water has hydrogen bonding as well as regular vanderwaals forces, therefore more energy is needed to overcome both types of intermolecular force instead of just overcoming Van der waals forcees. There water has a high bp.
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Name two properties of water apart from high boiling point.
Relatively high surface tension and high viscosity
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How are permanent dipole-dipole forces created?
Permanent dipole-dipole forces are created when neighbouring permanent dipoles on polar molecules attract eachother.
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What are the relative strength of the different types of bond?
Van der Waals forces: relative strength is 1. Ionic and covalent bonds: relative strength is 1000. Hydrogen bonds relative strength is 100. Dipole-dipole forces: relative strength is 10.
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Other cards in this set

Card 2

Front

How does atomic radius affect ionisation energy?

Back

The greater the atomic radius, the smaller the nuclear attraction experienced by the outer electrons, the smaller the ionisation energy.

Card 3

Front

How does nuclear charge affect ionisation energy?

Back

Preview of the front of card 3

Card 4

Front

How does electron shielding affect ionisation energy?

Back

Preview of the front of card 4

Card 5

Front

How many electrons can occupy the third shell?

Back

Preview of the front of card 5
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