chapter 6 Flashcards
compound
- a pure substance
- made of two or more different elements
that are chemically combined
2 types of compounds:
1) ionic compound
2) molecular compound
chemical bond
- a chemical link between two atoms,
which holds the atoms together
2 types of chemical bonds:
1) ionic bond
2) covalent bond
Recall
– a full outer energy level contains 8 electrons (like
the noble gases)
– a full outer energy level provides more chemical
stability / less reactivity
– atoms can achieve a full outer energy level by
gaining, losing, or sharing electrons with another
atom during a chemical reaction
Reactivity
- an element is stable when it has 8 electrons in
the outer shell (octet rule)
– except hydrogen (H), helium (He), lithium (Li) and
beryllium (Be) which are stable with 2 electrons in the
outer shell
Reactivity 2
- The closer to a full electron shell an atom is,
the more reactive it is
– more reactive means the atom is more likely to
take part in a chemical reaction to form a
compound
– less reactive means the atom is less likely to take
part in a chemical reaction to form a compound
Ions
- When atoms lose or gain electrons, they
become ions.
– **Cations **are positive and are formed by elements
on the left side of the periodic chart (metals).
– Anions are negative and are formed by elements
on the right side of the periodic chart (non-metals).
– Hydrogen is unique due to its 1 valence electron
(can form a cation or an anion).
ion charge=
protons + electrons
ions charges examples
eg.lithium atom:3 protons 3 electrons 0charge
loss of electrons=(lithum ion)3protons 2electrons 1+ charge
* e.g. sodium ion has 11 protons (+11) and 10
electrons (-10) for a charge of +1, represented
as Na+
Halogens (group 17)
➢ all atoms have 7 valence electrons.
➢ need to gain 1 electron to have a
stable octet.
➢ form anions.
➢ Ions will have a charge of 1-.
Alkali Metals (group 1)
➢ all atoms have 1 valence electron.
➢ need to lose 1 electron to have a
stable octet.
➢ form cations.
➢ Ions will have a charge of 1+.
Alkaline Earth Metals (group 2) .
➢ all atoms have 2 valence electrons.
➢ need to lose 2 electrons to have a
stable octet.
➢ form cations
➢ Ions will have a charge of 2+,
Ionic Compounds
When an ionic compound forms, the metal
atom donates its valence electrons to the
non-metal atom in order for both atoms
to form a stable octet.
Example: sodium and chlorine combine
to form sodium chloride, NaCl
An ionic bond involves the transfer of one or
more electrons.
Remember: Metals are electron donors.
Non-metals are electron acceptors.
Ionic Bonds
Ionic compounds (such as NaCl) are
generally formed between metals and
nonmetals.
Ionic bond
- a chemical bond that forms by
the attraction between
oppositely charged ions
(electrostatic forces) - Involves a transfer of electrons:
(Metals are electron donors;
non-metals are electron
acceptors. - strong but weaker than
covalent bonds - require a lot of energy to break
Drawing BR diagrams for ionic compound
- Magnesium loses 2
electrons for an ionic
charge of 2+ - Oxygen gains 2 electrons
for an ionic charge of 2- - Remember the ionic
charges should cancel out
to leave the ionic
compound neutral (NO
charge). - See BLM 6-5 and your
textbook for additional
examples.
magnesium oxide, MgO
Don’t forget to draw the nucleus
correctly with protons and neutrons.
