Init 10/10/2011 by Daniel R. Barnes
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covalent
metallic
ionic
. . . compare and contrast ionic bonding, metallic bonding, and covalent bonding.
* when a metal bonds with a nonmetal
* Nonmetal takes electrons from the metal.
* non-conducting when solid, but conductive when molten from high temp. OR when dissolved in water
* forms ionic crystals
* Positive cations are attracted to negative anions.
* No sharing of electrons. Electrons are given and taken, not shared. Nonmetals cling hard to the electrons they take.
* Material tends to be hard, brittle solid with a high melting and boiling point. Crystals may glitter, but material is not lustrous.
Na+ Cl-
Na+Cl-
Na+ Cl-
Na+Cl-
Na+ Cl-
Na+Cl-
Na+ Cl-
Na+Cl-
Na+ Cl-
Na+Cl-
Na+ Cl-
Na+Cl-
Na+ Cl-
Na+Cl-
Na+ Cl-
Na+Cl-
Na+ Cl-
Na+Cl-
Na+ Cl-
Na+Cl-
Na+ Cl-
Na+Cl-
Na+ Cl-
Na+Cl-
Na+ Cl-
Na+Cl-
Na+ Cl-
Na+Cl-
Na+ Cl-
Na+Cl-
Na+ Cl-
Na+Cl-
Na+ Cl-
Na+Cl-
Na+ Cl-
Na+Cl-
Na+ Cl-
Na+Cl-
Na+ Cl-
Na+Cl-
Na+
Cl-
Na+
Cl-
Na+
Cl-
Na+
Cl-
Ionic crystals tend to be brittle. If you smack them with a hammer, they tend to shatter
Cl-
Na+
Na+ Cl-
Na+Cl-
Cl-
Na+
Na+
Cl-
Na+
Cl-
Na+ Cl-
Na+Cl-
In this salt crystal, +’s are next to –’s, so everybody is attracted to their nearest neighbors, causing the crystal to stay together.
If you smack it with a hammer . . .
The part of the crystal you hit will dislocate and slide until + is next to + and – is next to -
This will cause the part that moved to be repelled by the part that didn’t move, breaking the crystal in two.
What do neighboring cations and anions feel for each other?
Cl-
Na+
Na+ Cl-
Na+Cl-
Cl-
Na+
Na+
Cl-
Na+
Cl-
Na+ Cl-
Na+Cl-
What do two +’s next to each other or two –’s next to each other feel?
* when a metal bonds with itself (pure metal) or another metal (alloy)
* Metal atoms give off electrons to become positive cations.
* Good conductors of heat and electricity, even when solid
* Forms metallic crystals, though these may be too small to see
Bismuth crystals
Brass microstructure
Sometimes, metal crystals are big enough to see. This is a mass of platinum crystals.
* when a metal bonds with itself (pure metal) or another metal (alloy)
* Metal atoms give off electrons to become positive cations.
* Good conductors of heat and electricity, even when solid
* Forms metallic crystals, though these may be too small to see
* Positive cations are attracted to negative “sea” of freely-flowing electrons in between the cations.
* Electrons given off by metal atoms are shared equally by all positive cations in the chunk of metal in question. They belong to everyone, yet to no one in particular. Electrons wander freely.
* Materials tend to be malleable solids with high melting and boiling points (although 1A are soft and Hg is liquid!).
Al3+ Al3+ Al3+ Al3+ Al3+
Al3+ Al3+ Al3+ Al3+Al3+
Al3+ Al3+ Al3+ Al3+ Al3+
Al3+ Al3+ Al3+ Al3+Al3+
Al3+ Al3+ Al3+ Al3+ Al3+
Al3+ Al3+ Al3+ Al3+Al3+
Al3+ Al3+ Al3+ Al3+ Al3+
Al3+ Al3+ Al3+ Al3+Al3+
NOTE: I’m not 100% sure if Al cations in a chunk of pure alumnimum really have a charge of 3+. I’m just guessing that based on their location on the PT.
* Happens when a nonmetal atom bonds with another nonmetal atom. Atoms can be same or different element.
* pairs of electrons shared between two atoms
* poor electrical conductors = “insulators”
* forms molecules (water, carbon dioxide, oil, plastic) or network solids (diamond, graphite).
* Positive nuclei are attracted to negative electrons shared between them.
* Electrons are shared exclusively and privately by the atoms that share them. No one else is involved. Electrons not free to wander.
* Material may be brittle, smushy, liquid, gaseous, elastic, or any number of possibilities.
HH
H H
Hydrogen gas is made of molecules, each of which is made of two atoms that are covalently-bonded to each other.
The two atoms in an H2 molecule share a pair of electrons.
The two atoms in this molecule share these two electrons with each other and only with each other.
Even if others molecules come very close, the atoms in this molecule share electrons only with each other, not with atoms from other molecules.
HH
still table saltNa+ Cl- Na+ Cl-
Na+ Cl-
Na+Cl-
table saltstill table salt
Na+
Cl-
Cl-
Na+
Na+Cl- Cl- Na+
Yep. It’s still table salt.Na8Cl8 = NaCl. Same stuff.
The ratio of sodium to chloride is the same (1:1), so it’s still the same chemical with the same properties.
A salt crystal can have twelve million sodium atoms, as long as it has twelve million chlorine atoms.
Cl-Na+ Na+ Cl-
Na+ Cl-
Na+Cl-
table saltNa+
Cl-
Cl-
Na+
Na+Cl- Cl- Na+
NaCl
HO
H
H2O
This is a water molecule.
HO
H
HO
HH4O2
This is NOT a water molecule.In fact, this is an unstable monster that would not exist for long.
BondType
Elementsbonded
Covalent NM & NM
Ionic Met & NM
Metallic Met & Met
Role ofelectrons
sharedexclusively
given &taken
sharedcommunally
ElectricalConductivity
varies but generally
poor
only when melted or dissolved
very conductive
Basis of bond
+ nuclei like
- shared electrons
+ cations like
- anions
+ cations like
- wandering electrons
Bond Type Comparison Summary Chart
Q1: In what kind of bonds are electrons shared?A: covalent and metallic
Q2: What kind of bond typically forms between a metal and a nonmetal?A: an ionic bond
Q3: What is bonding, anyway?A: when atoms stick to each other really hard
Q4: Why are metals good conductors?A: The shared electrons are free to wander from atom to atom. They form a “sea” of electrons that can flow.
Q5: What is a covalent bond made of?A: one or more shared pairs of electrons
Q6: How can you make a salt crystal conduct electricity?A: melt it with extreme heat or dissolve it with waterQ7: Salt is made of positive and negative ions. What is made only of positive ions?A: metals
Q8: What do you call a mixture of two or more different metals?A: an “alloy”Q9: Give an example of an alloy and what it’s made of.A: Many examples are possible, including bronze, which is made of copper & tin, or brass (Cu & Zn).
Q10: What do you call a small cluster of nonmetal atoms covalently bonded together?A: a “molecule”
