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chemical bonding Flashcards

(107 cards)

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1
Q

What is electronegativity?

A

The ability of an atom to attract a pair of electrons towards itself in a covalent bond

This arises from the positive nucleus’s ability to attract negatively charged electrons in the outer shells.

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2
Q

What scale is used to assign electronegativity values?

A

The Pauling scale

It assigns a value of electronegativity for each atom.

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3
Q

Which element is the most electronegative on the Periodic Table?

A

Fluorine with a value of 4.0 on the Pauling Scale.

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4
Q

How does electronegativity generally change across a period?

A

Electronegativity increases across a period.

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5
Q

How does electronegativity generally change down a group?

A

Electronegativity decreases down a group.

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6
Q

What effect does nuclear charge have on electronegativity?

A

An increased nuclear charge results in increased electronegativity.

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7
Q

What is the relationship between atomic radius and electronegativity?

A

An increased atomic radius results in decreased electronegativity.

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8
Q

What is shielding in the context of electronegativity?

A

Shielding refers to filled energy levels masking the effect of nuclear charge on outer electrons.

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9
Q

True or False: Sodium has a higher electronegativity than caesium.

A

True.

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10
Q

What happens to electronegativity as you move down a group in the Periodic Table?

A

It decreases due to increased shielding and atomic radius.

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11
Q

What is the trend in electronegativity as you move across a period?

A

It increases due to increased nuclear charge and consistent shielding.

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12
Q

Fill in the blank: The general trend is an increase in electronegativity towards the _______.

A

top right of the Periodic Table.

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13
Q

How can electronegativity differences predict bond formation?

A

They indicate whether a bond is covalent or ionic in character.

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14
Q

What type of bond is formed when both atoms have the same electronegativity?

A

A non-polar covalent bond.

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15
Q

What results from a significant difference in electronegativity between two atoms?

A

The formation of an ionic bond.

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16
Q

What is an ionic bond?

A

The electrostatic attraction between oppositely charged ions.

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17
Q

What type of ions do metals typically form?

A

Positively charged cations.

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18
Q

What type of ions do non-metals typically form?

A

Negatively charged anions.

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19
Q

What is the electronic configuration of a potassium ion (K+)?

A

[2,8,8]+.

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20
Q

What is a lattice structure in ionic compounds?

A

An evenly distributed crystalline structure with alternating cations and anions.

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21
Q

What is the charge of sodium chloride (NaCl)?

A

Neutral.

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22
Q

What happens in the ionic bonding of magnesium oxide (MgO)?

A

Magnesium loses 2 electrons to form Mg2+, and oxygen gains 2 electrons to form O2-.

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23
Q

In calcium fluoride (CaF2), how many fluoride ions are needed for each calcium ion?

A

Two fluoride ions.

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24
Q

What are delocalised electrons?

A

Electrons that are free to move throughout a metallic lattice structure.

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25
What occurs during covalent bonding?
Electrons are shared between two nonmetals.
26
What allows non-metals to achieve a noble gas electron configuration in covalent bonds?
The sharing of pairs of electrons.
27
What is a covalent bond?
A covalent bond involves the electrostatic attraction between nuclei of two atoms and the bonding electrons of their outer shells
28
How do electrons behave in covalent bonding?
No electrons are transferred but only shared in this type of bonding
29
What allows non-metals to form covalent bonds?
Non-metals are able to share pairs of electrons to form different types of covalent bonds
30
What is the result of sharing electrons in covalent bonds?
Each of the 2 atoms can achieve an electron configuration similar to a noble gas, making each atom more stable
31
What is a single covalent bond?
A bond formed by sharing one pair of electrons
32
How many electrons are shared in a double covalent bond?
4 electrons
33
How many electrons are shared in a triple covalent bond?
6 electrons
34
What do dot and cross diagrams represent?
They represent covalent bonding, showing just the outer shell of the atoms involved
35
In a dot and cross diagram, how are electrons differentiated?
Dots for electrons of one atom and crosses for electrons of the other atom
36
What is the composition of the hydrogen molecule (H2)?
Contains a single covalent bond due to one shared pair of electrons
37
How do chlorine atoms form a chlorine molecule (Cl2)?
By sharing their unpaired outer electrons, resulting in a single covalent bond
38
What type of bond is formed between hydrogen and chlorine in HCl?
A single covalent bond due to one shared pair of electrons
39
How is ammonia (NH3) formed?
Each hydrogen atom pairs its outer electron with each of the unpaired electrons from nitrogen, forming three single covalent bonds
40
What is the structure of methane (CH4)?
Contains four single covalent bonds due to four shared pairs of electrons
41
How does ethane (C2H6) form its bonds?
Each carbon atom shares one of its unpaired electrons with the other carbon atom, forming a single covalent bond
42
What is the composition of the oxygen molecule (O2)?
Contains a double covalent bond due to two shared pairs of electrons
43
How is carbon dioxide (CO2) structured?
Contains two double covalent bonds due to two sets of two shared pairs of electrons
44
What defines a triple covalent bond in nitrogen (N2)?
Formed by sharing three pairs of electrons
45
What is meant by 'expanding the octet rule'?
The ability of a central atom in a covalently bonded molecule to accommodate more than 8 electrons in its outer shell
46
What happens in sulfur dioxide (SO2) regarding the octet rule?
Sulfur has an expanded octet as it shares 10 electrons
47
What is dative covalent bonding?
A type of bonding where both electrons in the bond come from the same atom
48
What is an example of dative covalent bonding?
Ammonium ion (NH4+) formed when ammonia donates a lone pair to an electron-deficient proton (H+)
49
What is hybridization in covalent bonding?
The mixing of atomic orbitals to form covalent bonds
50
What is sp3 hybridization?
Mixing one s orbital with three p orbitals
51
What is the difference between sigma (σ) and pi (π) bonds?
σ bonds are formed by direct overlap of orbitals, while π bonds are formed by sideways overlap of adjacent p orbitals
52
What defines a molecular orbital?
A combined orbital containing two electrons formed by overlapping atomic orbitals
53
How is ethylene (C2H4) structured?
Contains one double bond (one σ and one π bond) and multiple single bonds
54
What is the structure of ethyne (C2H2)?
Contains a triple bond formed from two π bonds and one σ bond
55
What is the bonding structure of hydrogen cyanide (HCN)?
Contains a triple bond formed from the overlap of p orbitals and hybridized orbitals
56
What is the role of lone pairs in coordinate bonding?
Lone pairs can be donated to form a bond with an electron-deficient atom
57
What is sp2 hybridisation?
Mixing one s orbital with two p orbitals ## Footnote It is used in molecules with trigonal planar geometry.
58
What forms sp hybridised orbitals?
Mixing one s orbital with one p orbital ## Footnote This is typically seen in linear molecular geometries.
59
What is hybridisation in terms of molecular bonds?
The mixing of s orbitals with p orbitals to form molecular bonds
60
Define bond energy.
The energy required to break one mole of a particular covalent bond in the gaseous states
61
What are the units of bond energy?
kJ mol-1
62
How does bond energy relate to covalent bond strength?
The larger the bond energy, the stronger the covalent bond is
63
What is bond length?
The internuclear distance of two covalently bonded atoms
64
What happens to bond length as the forces of attraction between electrons and nuclei increase?
The bond length decreases and the strength of the covalent bond increases
65
Which type of bond is the shortest and strongest?
Triple bonds
66
What factors influence the reactivity of covalent molecules?
The bond polarity, bond strength, and bond type (σ/π)
67
What trend is observed in bond energy values of hydrogen halides from HCl to HI?
They decrease in the order HCl > HBr > HI
68
Why does the bond energy decrease in hydrogen halides down the group?
Atoms get bigger, reducing the attractive force between bonding electrons and the nucleus
69
What is VSEPR theory?
The valence shell electron pair repulsion theory predicts the shape and bond angles of molecules
70
What do lone pair electrons do in relation to bonded pairs?
Lone pair electrons repel each other more than bonded pairs
71
What is the order of repulsion between electron pairs?
lone pair – lone pair > lone pair – bond pair > bond pair – bond pair
72
What shape does phosphorous(V) chloride (PCl5) adopt?
Trigonal bipyramidal
73
What shape does nitrogen in N(CH3)3 adopt?
Pyramidal
74
What shape does carbon in CCl4 adopt?
Tetrahedral
75
What is hydrogen bonding?
The strongest form of intermolecular bonding
76
What conditions must be met for hydrogen bonding to occur?
1. A highly electronegative atom (O, N, or F) with a lone pair. 2. A hydrogen atom covalently bonded to O, N, or F.
77
How many hydrogen bonds can ammonia form?
One hydrogen bond per molecule
78
How many hydrogen bonds can water form?
Two hydrogen bonds per molecule
79
What causes water to have high melting and boiling points?
Strong intermolecular forces of hydrogen bonding
80
What is the effect of hydrogen bonding on the density of ice compared to liquid water?
Ice has a lower density than liquid water
81
What is electronegativity?
The ability of an atom to draw a pair of electrons towards itself in a covalent bond
82
When is a covalent bond considered nonpolar?
When two atoms have the same electronegativity
83
What happens when two atoms in a covalent bond have different electronegativities?
The bond becomes polar, with an asymmetric electron distribution
84
Define dipole moment.
A measure of how polar a bond is
85
How is the direction of a dipole moment represented?
By an arrow pointing to the partially negatively charged end of the dipole
86
What are van der Waals' forces?
Weaker intermolecular forces between molecules
87
What are the two types of van der Waals’ forces?
* Instantaneous dipole – induced dipole forces (London dispersion forces) * Permanent dipole – permanent dipole forces
88
What is the relationship between the polar covalent bonds in water and the intermolecular forces?
Polar covalent bonds are intramolecular forces and permanent dipole – permanent dipole forces are intermolecular forces
89
What are instantaneous dipole - induced dipole forces also known as?
London dispersion forces ## Footnote These forces exist between all atoms or molecules.
90
What causes a temporary dipole to arise in non-polar molecules?
The constant movement of the electron charge cloud ## Footnote This movement can result in an uneven distribution of electron density.
91
What happens when a temporary dipole induces a dipole in neighboring molecules?
The δ+ end of one dipole is attracted to the δ- end of the neighboring dipole.
92
How do id-id forces change with the number of electrons in a molecule?
Id-id forces increase with increasing number of electrons and atomic number.
93
What effect does the number of contact points have on id-id forces?
Increasing the number of contact points leads to more id-id forces.
94
What defines a permanent dipole in a molecule?
A molecule has a permanent dipole when it has a negatively and positively charged end.
95
What are the forces between two molecules with permanent dipoles called?
Permanent dipole - permanent dipole forces.
96
Which type of intermolecular forces is stronger for small molecules with the same number of electrons?
Permanent dipole - permanent dipole forces are stronger than instantaneous dipole - induced dipole forces.
97
What is a key difference between intramolecular and intermolecular forces?
Intramolecular forces are forces within a molecule, while intermolecular forces are forces between molecules.
98
What is hydrogen bonding?
An intermolecular force between molecules with -OH/-NH groups and molecules with N/O atoms.
99
How does hydrogen bonding compare to permanent dipole - permanent dipole forces?
Hydrogen bonds are stronger than permanent dipole - permanent dipole forces.
100
What is the general trend of bond strength from strongest to weakest?
Ionic bonding > Hydrogen bonding > Permanent dipole - permanent dipole > Instantaneous dipole - induced dipole.
101
What are dot and cross diagrams used for?
To show the arrangement of outer-shell electrons in ionic or covalent compounds.
102
How are ionic bonds formed?
Metal atoms transfer electrons to non-metal atoms to form cations and anions.
103
What defines a covalent bond?
The sharing of outer valence electrons between atoms.
104
What is coordinate (dative) covalent bonding?
Bonding formed when one atom provides both electrons for a covalent bond.
105
What is the incomplete octet rule?
Some species may have less than eight electrons in their outer shell.
106
What is the expanded octet rule?
Some species may contain more than eight electrons in their outer shell.
107
What can dot-and-cross diagrams show regarding odd numbers of electrons?
They can show compounds containing atoms with an odd number of outer electrons.

Chemistry AS (9 decks)

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