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chemistry > unit 7 - bonding > Flashcards

unit 7 - bonding Flashcards

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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
Q

covalent bonds

A

involve the sharing of valence electrons between 2 non-metals
- no ions are involved; only molecules = covalent

26
Q

4 types of Covalent Bonds:

A
  1. non-polar covalent
  2. polar covalent
  3. co-ordinate covalent
  4. network covalent
27
Q

properties of covalent bonds

A
  • 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
Q

non polar covalent bonds

A
  • 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
Q

polarity

A
  • refers to charge; so Non-Polar refers to NO DIFFERENCE in charge
30
Q

the electronegativity difference for nonpolar covalent bonds is

A

zero

31
Q

allotropes

A
  • 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
Q

polar covalent bonds

A
  • a bond in which atoms of 2 different non metals share electrons unequally
33
Q

electronegativity difference of polar covalent bonds

A

is between 0 & 1.7

34
Q

compounds that are composed of both IONIC AND COVALENT BONDS contain

A

POLYATOMIC IONS

35
Q

co-ordinate covalent bonds

A
  • AKA: free loader bond
  • one atom supplies both electrons (lone pair) to be shared

ex: ammonia + proton -> ammonium ion
water + proton -> hydronium ion

36
Q

network bonds

A
  • 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
Q

metallic bonds

A
  • 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
Q

bond types

A

metallic, ionic, covalent (network, polar, nonpolar, co-ordinate)

39
Q

molecule type

A

polar molecule, nonpolar molecule

40
Q

nonpolar molecules have

A

EQUAL charge distribution and are SYMMETRICAL molecules
** bond type does not always match molecule type

41
Q

nonpolar molecule examples

A

LINEAR:
- CO2, H2, O2, N2, Cl2, Br2, F2, I2

TETRAHEDRAL:
- CH4, SiBr4, CCl4, SH4

42
Q

polar molecules

A
  • have unequal/uneven charge distribution
  • are NOT symmetrical
43
Q

polar molecule examples (linear)

A

HF, HCl, HI, HBr

44
Q

polar molecule examples (tetrahedral)

A

CH3Cl, CH2Cl2, SiH3Cl, SiH2Cl2

45
Q

polar molecule examples (bent)

A

H2O, H2S, H2Se, H2Te

46
Q

polar molecule examples (pyramidal)

A

NH3, PH3, AsH3

47
Q

SNAP

A
  • SYMMETRICAL - NONPOLAR molecule
  • ASYMMETRICAL - POLAR molecule
48
Q

intramolecular

A

A bond WITHIN a molecule

49
Q

Intermolecular

A

A bond between molecules

50
Q

Intermolecular Force: Dipole-Dipole

A

Bond between 2 identical polar molecules

51
Q

Hydrogen Bonding

A
  • (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
Q

Hydrogen Bonding characteristics

A
  • 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
Q

Van der Waals Forces

A
  • 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
Q

When is van der waals forces most effective

A

Most effective when molecules are close such as between molecules with more electrons and a larger molecular mass

55
Q

The STRONGER the Van der Waals force

A

the HIGHER the melting/boiling point of the substance

56
Q

MOLECULE/ION ATTRACTION

A
  • 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
Q

Ionic substances (salt) dissolve in

A

Polar substances

58
Q
A

chemistry (11 decks)

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