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unit 7 - bonding Flashcards

1
Q

chemical bond

A

an attraction between atoms for electrons

(electronegativity)

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2
Q

a chemical bond involves what

A

attraction between nuclei for electrons

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3
Q

when forming a bond, electrons may be…

A

lost, gained, or shared

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4
Q

The # of electrons in a chemical bond is such that each atom fills its valence shell

A
  • 8 electrons fill the valence shell (Most elements).
  • Some exceptions: Ex. H and He need only 2
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5
Q

He and H only need how many valence electrons for full valence shell

A

2 electrons

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6
Q

when a bond is broken, what happens to heat

A

heat energy is absorbed
(endothermic process)

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7
Q

when a bond is formed, heat energy is

A

released
(exothermic process)

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8
Q

if sign on table I is “-“ , reaction is overall

A

exothermic

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9
Q

Heats of Reaction:

Ex. H2 + I2 +53 KJ => 2 HI

A
  • Endothermic (Energy is on Left/Absorbed)
  • More energy used to break bonds
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10
Q

Heats of Reactions

Ex. 2 H2 + O2 => 2 H2O + 483.6 KJ

A
  • Exothermic (Energy is on Right/Released)
  • More energy released in forming bonds
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11
Q

potential energy

A

Amount of Energy stored within the bonds (distance between the atoms involved in the bond)

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12
Q

When more energy is used to break bonds Reaction is (endo) –> PE

A

increases

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13
Q

When more energy is used to form bonds Reaction is (exo) –> PE

A

decreases

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14
Q

Ionic Bonds

A

Form when metals transfer valence electrons to non-metals.

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15
Q

Ionic Bonds are formed from the

A

attraction between positive and negative ions

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16
Q

Ionic Substances are called

A

Ionic Compounds NOT molecules
Ex. All Salts

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17
Q

why aren’t ionic substances called molecules

A

molecules have neutral particles

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18
Q

Ionic bond characteristics

A
  • ionic bonds are very strong
  • ions are held in a fixed position in a “crystal lattice structure”
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19
Q

Ionic compounds are what at room temp?

A

Solids at room temp

  • high melting points (ex: NaCl = 801C, KCl = 771C)
  • high boiling points (ex: NaCl = 1465C, KCl =1420C
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20
Q

Ionic compounds are:

A
  • poor conductors as solids
  • good conductors when melted (molten)
  • soluble in polar solvents (ex. Water)
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21
Q

why are ionic compounds good conductors when dissolved

A

good conductors when dissolved in water because ions are free to carry a current

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22
Q

ionic bonds

A

form when elements with large differences in electronegativity combine

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23
Q

if the difference in electronegativity is 1.7 or greater

A

ionic bond

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24
Q

the greater the difference in E.N.

A

the stronger the Ionic Bond

25
covalent bonds
involve the sharing of valence electrons between 2 non-metals - no ions are involved; only molecules = covalent
26
4 types of Covalent Bonds:
1. non-polar covalent 2. polar covalent 3. co-ordinate covalent 4. network covalent
27
properties of covalent bonds
- aka molecular substances - most are poor conductors in all three phases of matter (inlcluding water) - have low melting/boiling points - weak forces hold molecules together
28
non polar covalent bonds
- no difference in electronegativity - involve the EQUAL sharing of electrons - electrons spend same amount of time in the valence shell of both atoms - form between 2 identical non-metal atoms ex: H2, O2, N2, etc.
29
polarity
- refers to charge; so Non-Polar refers to NO DIFFERENCE in charge
30
the electronegativity difference for nonpolar covalent bonds is
zero
31
allotropes
- different forms of the same element ** different physical properties (color, shape, hardness, melting point) due to *different arrangement of atoms with different structure - ex: diamonds & graphite (all carbon) - ex: oxygen (O2) and ozone (O3) - **all have non polar covalent bonds
32
polar covalent bonds
- a bond in which atoms of 2 different non metals share electrons unequally
33
electronegativity difference of polar covalent bonds
is between 0 & 1.7
34
compounds that are composed of both IONIC AND COVALENT BONDS contain
POLYATOMIC IONS
35
co-ordinate covalent bonds
- AKA: free loader bond - one atom supplies both electrons (lone pair) to be shared ex: ammonia + proton -> ammonium ion water + proton -> hydronium ion
36
network bonds
- consists of special covalently bonded atoms in a network - no separate particles, considered one giant "macro-molecule" - strong bonds; ultra high melting points ex: diamonds - poor conductors, very hard substances (generally) - ex: diamond (carbon), graphite (carbon), SiO2 (quartz), and SiC (silicon carbide)
37
metallic bonds
- bonds that hold metal atoms together - very strong bonds - "+" nuclei in a "sea of mobile electrons" - free moving electrons give metals luster and conductivity - metals are good conductors in all three states of matter
38
bond types
metallic, ionic, covalent (network, polar, nonpolar, co-ordinate)
39
molecule type
polar molecule, nonpolar molecule
40
nonpolar molecules have
EQUAL charge distribution and are SYMMETRICAL molecules ** bond type does not always match molecule type
41
nonpolar molecule examples
LINEAR: - CO2, H2, O2, N2, Cl2, Br2, F2, I2 TETRAHEDRAL: - CH4, SiBr4, CCl4, SH4
42
polar molecules
- have unequal/uneven charge distribution - are NOT symmetrical
43
polar molecule examples (linear)
HF, HCl, HI, HBr
44
polar molecule examples (tetrahedral)
CH3Cl, CH2Cl2, SiH3Cl, SiH2Cl2
45
polar molecule examples (bent)
H2O, H2S, H2Se, H2Te
46
polar molecule examples (pyramidal)
NH3, PH3, AsH3
47
SNAP
- SYMMETRICAL - NONPOLAR molecule - ASYMMETRICAL - POLAR molecule
48
intramolecular
A bond WITHIN a molecule
49
Intermolecular
A bond between molecules
50
Intermolecular Force: Dipole-Dipole
Bond between 2 identical polar molecules
51
Hydrogen Bonding
- (special dipole-dipole) - a bond BETWEEN a hydrogen atom of one molecule (polar molecule) and a highly electronegative atom Ex: (F, O, N) of another molecule Ex. Between molecules of HF, H2O, and NH3
52
Hydrogen Bonding characteristics
- Strong bonds (strong intermolecular force) - Reason why water has a high melting point/high boiling point for its size - the stronger the intermolecular force, the higher the boiling point
53
Van der Waals Forces
- attraction between non polar molecules (symmetrical) - weak force of attraction so low melting and boiling point - reason why non polar molecules exist as liquids at low temperature and high pressure - ex: if a solid and gas at same temperature, gas has weaker intermolecular force
54
When is van der waals forces most effective
Most effective when molecules are close such as between molecules with more electrons and a larger molecular mass
55
The STRONGER the Van der Waals force
the HIGHER the melting/boiling point of the substance
56
MOLECULE/ION ATTRACTION
- attraction between a + or – ion (ionic compound) and the opposite charged ends of a solvent molecule (a liquid in which a substance dissolves) Ex: H2O and NaCl
57
Ionic substances (salt) dissolve in
Polar substances
58

chemistry (11 decks)

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