Chemical Bonding Flashcards
Chemical Bond
an attraction between atoms for electrons
A chemical bond involves:
- attraction between nuclei for electrons
- electrons may be lost, gained, or shared when forming a bond
- the # of electrons in a chemical bond is such that each atom fills its valence shell
- 8 electrons fill the valence shell expect H and He only need 2
When a bond is broken..
heat energy is absorbed and it’s an endothermic process
When a bond is formed…
heat energy is released and it’s an exothermic process
When energy is on left.. H2 + I2 + 53 KJ -> HI
more energy is absorbed to break bonds so it’s endothermic
When energy is on right.. H2 + I2 -> H20 + 483.6 KJ
more energy is released in forming bonds so its exothermic
Potential Energy
amount of energy stored within the bonds (distance between the atoms involved in the bond)
When more energy is used to break bonds reaction is (endo) the potential energy
increases
When more energy is used to form bonds reaction is (exo) the potential energy
decreases
with endothermic the…
- potential energy increases
- breaking bonds
- less stable process
- easy to decompose
with exothermic the…
- potential energy decreases
- forming bonds
- more stable process
- hard to decompose
Ionic Bonds
form when metals transfer valence electrons to non-metals
Ionic bonds are formed from the attraction between
positive and negative ions
Ionic Substances are called
ionic compounds not molecules because molecules have neutral particles
Ionic Bond Characteristics
- ionic bonds are very strong
- ions are held in a fixed position in a “crystal lattice structure.”
- ionic compounds are solids at room temp
- they have high melting points and high boiling points
Ionic Compounds are
poor conductors as solids, good conductors when melted, good conductors when dissolved in water because ions are free to carry a current; soluble in polar solvents (ex. H2O)
Ionic bonds form when
elements with large differences in electronegativity combine (difference 1.7 or greater ) - the stronger the ionic bond the greater the difference in EN
ionic bonds have what type of diagram?
simple lewis dot diagram so like Br with it’s number of valency electrons or A metal with it;s ions and then a non metal with brackets.
Covalent Bonds
involve the sharing of electrons between 2 non- metals - no ions are involved only molecules
Properties of Covalent Bonds
A.K.A molecular substances (neutral)
most are poor conductors in all three phases of matter - including water (ex. Sugar) - low melting and boiling points
weak forced hold molecules together
Non Polar Covalent Bonds
involve equal sharing of electrons (electrons spend same amount of time in the valence shell of both atoms )
form between 2 identical non-metals atoms - diatomics
Polarity
refers to charge ; so non polar refers to no difference in charge - the electronegativity difference is always 0
Allotropes
are different forms of an element - different physical properties due to different arrangement of atoms with different structure (diamond, graphite + oxygen and ozone)
Polar covalent bonds
a bond in which atoms of 2 different non-metals share electrons unequally - electronegativity difference is between 0 and 1.7
