Bonding Flashcards

1
Q

Why is ice less dense than water ?

A

ice molecules arrange themselves in a rigid tetrahedral structure ( hexagonal rings) which causes big gaps in their bonding. on the other hand water molecules remain in linear bonding form so molecules are held a lot closer together ( by hydrogen bonds)

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2
Q

How does ion charge affect melting point

A

the greater the charge on the ion the greater the electrostatic attraction ( stronger ionic bond) so more energy is needed to break the bonds. hence a higher melting point.

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3
Q

Which has the highest medium and lowest mp out of sodium, magnesium and potassium ?

A

Mg has the highest mp because it forms a 2+ charge unlike the other two group 1 metals. Then sodium because it is in period 2 and so has a higher charge density due to less shells ( more positive charge concentrated on fewer electron shells) and finally potassium which has a lower charge density because it is in period 3 and has more shells

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4
Q

What is a coordinate/ dative bond ?

A

a normal covalent bond, but one molecule supplies both electrons. on a displayed formula a dative bond is shown by an arrow

acceptor atom receiving eelctrons must be electron deficient for dative bond to form

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5
Q

What is an ionic bond ?

A
  • the force of electrostatic attraction, not the transfer of electrons ( that is how ionic bond is formed)
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6
Q

What is electronegativity

A

ability of an atom to attract the electron pair in s covalent bond to itself

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7
Q

What is a polar bond vs a non polar bond

A
  • different atoms with different electronegativities, one will pull on electron pair more, so will have a slight neg charge, other slightly pos charge. Dipole formed and bond is said to be polar

non polar - similar atoms have the same electronegativity so will both pull on electrons to the same extent meaning they are equally shared.

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8
Q

What is Pauling scale

A

a scale for measuring electronegativity. 4 will have the highest electrnegativity

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9
Q

What is a permanent dipole

A
  • regions of partial positive and negative charge within same molecule
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10
Q

How can dipoles interact

A
  • attract the opposite charges on neighbouring molecules
  • slight positive reg would attract slight negative reg on neighbour molecule
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11
Q

What is a hydrogen bond ?

A
  • attraction between slight positive charge on one atom of molecule and lone pair of electrons
  • very strong
  • hydrogen must be directly bonded to electronegative element ie oxy, fluorine and there must be a lone pair of electrons not bonded present
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12
Q

how are temporary dipoles formed?

A
  • when two atoms come towards each other electrons repel each other
  • causes sudden displacement of electrons to one side, causing atom to have a temp dipole
  • side where electrons have moved to would have slight neg charge and other side would have a slight pos charge.
  • this is known as an instantaneous dipole
  • this atom can now repel another atom and cause a shift in its electrons to one side, thus inducing a dipole ( not the same as an instantaneous dipole)
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13
Q

What are the three types of intermolecular forces and which are the strongest and weakest

A

permanent dipoles, hydrogen bonding and induced dipole

strongest is hydrogen bonding and weakest is induced dipole

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14
Q

How does electronegativity progress accross a period

A
  • across period from left to right electronegativity of atoms increases due to them having a greater number of protons to more strongly attract electrons in the covalent bond
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15
Q

How does electronegativity progress down a group ?

A
  • decreases because atoms have more energy levels and so shielding effect is increased, therefore harder to pull attract electrons in covalent bond
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16
Q

A molecule may be non polar even if it has polar bonds. How is this determined?

A
  • if molecule is symmetrical will usually be non polar because dipoles do cancel out
17
Q

Where are temporary dipoles also known as London forces found ?

A

all molecules

18
Q

How does hydrogen bonding affect water properties

A
  • high boiling point of water due to strong hydrogen bonds
  • ice less dense than water due to water molecules being further apart than in liquid water. In ice water molecules are arranged in a ordered structure stabilised by network of hydrogen bonds
19
Q

What are simple molecules

A
  • small molecules with a fixed number of atoms
20
Q

What does the solid line tell you in a compound? ( the solid lines representing the bonds)

A

tells you that the two bonds lie on the plane of the screen or the page

21
Q

What does the solid wedge shape tell you ?

A

Bond is coming out of the plane of the page

22
Q

What does a dotted wedge tell you?

A

bond is projecting back behind the plane of the page

23
Q

What does electron pair repulsion theory state?

A

The shape of the molecule is determined by the electron pairs surrounding the central atom. only refers to the outer shells in this case because pairs of electrons repel all of the other electron pairs.

24
Q

What does the repulsion of the electrons cause ?

A

Move as far apart as possible to minimise repulsion, and assume a shape that most minimises this.

25
Q

If you have BeCl2 what would the shape look like?

A

would be linear because there are two pairs of electrons ( covalent bonds) surrounding the central atom. So they will push as far away from each other as possible the furthest they can get is 180 degrees.

26
Q

When looking at double or triple bonds how do you treat the bonding area?

A

You treat it as a single bonding area and so therefore even if there is a double or triple bond this doesn’t affect the shape of the molecule

27
Q

If you have BF3 what does the shape of the molecule look like?

A

Central boron atom bonded to three fluorine atoms, in a trigonal planar shape which has a bond angle of 120 degrees.

28
Q

When will you have a trigonal planar compared to a linear shape of a molecule?

A
  • If you have a central atom bonded to three pairs of electrons you will have a trigonal planar shape while otherwise if you have two pairs of electrons you will have a linear shape. ( 180 degrees) if no lone pairs
29
Q

What are the bond angles in a tetrahedral molecule ?

A

109.5 degrees

30
Q

What if the central atom has 5 pairs of electrons

A

Two of the bonding pairs move to opposite sides of the molecule to minimize repulsion. The other three bonding pairs now take up a central position lying on the same plane, and spread themselves out as far as they can.

31
Q

What are the bond angles if the central atom has 5 pairs of electrons?

A

two bond angles to consider, one of which is 90 degrees and the other one of 120 degrees. the shape is trigonal bipyramidal because the base is a triangle and two pyramids are formed between the other atoms, one above and one below the plane.

32
Q

What is the shape of a molecule with 6 electron pairs around the central atom?

A

octahedral shape, bonding pair above and below the central plane, and 4 bonding pairs lying on the central plane. Bonds pointing up and down at 9-0 degrees to CP angle between bonds lying on CP also 90 in this case.

33
Q

Do dative bonds have an effect on the shape of a molecule?

A

No they don’t

34
Q

What can be said about lone pairs compared to bonding pairs?

A

Lone pairs repel more strongly, extra repulsion decreases bond angles by 2.5 degrees.

35
Q

What is the shape of H20 ( water) taking into account lone pairs of electrons?

A

oxygen has two lone pairs of electrons because has 6 valence electrons and only 2 used up in bonding. One lone pair reduces the bond angle by 2.5 degrees, so all together would be reduced by 5 degrees so the bond angle is reduced to 104.5 degrees instead of 109 degrees. shape is tetrahedral because there are 4 bonding areas ( 4 pairs of electrons)

36
Q

What is the difference between tetrahedral and square planar shape

A
  • square planar is basically the same, only difference is that with sq planar shape there are two lone pairs on central atom.
37
Q

hydrogen bonding occurs when ?

A

between hydrogen and either fluorine, nitrogen or oxygen

38
Q
A