Bonding Flashcards
Metallic bonding
A lattice of positively charged ions (cations), surrounded by free- moving,‘delocalised’ electrons.
Properties of metallic bonding
Because of their structure and bonding, Metals are:
•Good conductors of electricity WHEN SOLID
•Good conductors of heat
•Malleable and Ductile
•High boiling points
•Hard and dense
Galvanising
The process of applying a protective zinc coating to steel or iron to prevent rusting
•prevents corrosive substance from reaching iron / steel and zinc corrodes first
Cation
Positively charged ion
Anion
Negatively charged ion
Ionic bond
- Ionic bonding occurs as the result of a metal atom donating its outer shell electrons to a non-metal atom.
- The metal becomes a Cation.
- The non-metal becomes an anion.
Properties of ionic compounds
- high melting and boiling points
- hard and brittle
- can only conduct electricity as molten
- arranged in an ionic lattice
Why are ionic solids brittle?
when distorted like charged ions move closer to each other and strong electrostatic repulsion shatter the solid.
Why ionic liquids (molten and solution) can conduct electricity
Because ions are free to move and carry a charge when not in a lattice
Why ionic compounds have high melting and boiling points?
Due to the strong ionic bonds in 3 dimensions which requires great amounts of energy to overcome the bonds.
Covalent bonding
when non metallic atoms combine to form either molecules or covalent lattices with the sharing of electrons
Dative covalent bond
a covalent bond in which both of the shared electrons are contributed by one atom only
Valence structure
These show bonds in the form of lines, with other outer shell electrons as dots. Single bonds have single lines
Double bonds have 2 lines
Triple bonds have 3 lines
Lewis Structure (Electron Dot Diagram
These show outer-shell electrons and shows how they share to form a bond.
Octet rule
atoms with an atomic number below 20 tend to combine so that they each have eight electrons in their valence shells, making the same electronic configuration as a noble gas.
Valence electrons
The electrons in the outermost (valence) principal energy level of an atom that can participate in the formation of chemical bonds with other atoms.
Atomic number
The number of protons in an atom which determines its chemical properties.
Mass number
Number of protons and neutrons in an atom
Expanded octet
A case where an atom shares more than eight electrons with its bonding partners.
•elements in period 3 group 5-7 can have greater than 8 electrons in valence shell
Electron pair repulsion theory
the shape of a molecule is determined by the number of electron pairs surrounding the central atom
•electrons repel and therefore arrange away from one another
Covalent networks
are non-metal substances that exist as giant, 3D arrays of atoms.
-graphite, diamond, silicon dioxide
Properties of covalent molecules
- Have low melting/boiling points - do not conduct electricity (no free moving electrons)
- have low solubility in water**
**there are a few exceptions i.e NH3, CH3COOH
Properties of covalent networks
- high melting and boiling point
- non-conductors of electricity (except Graphite) or heat
- very hard substances
- insoluble in water
Properties of diamond
- Giant lattice of carbon atoms covalently bonded to 4 others in tetrahedral arrangement
- high melting and boiling points
- does not conduct electricity
- insoluble in water
Properties of silicon dioxide
- arranged tetrahedrally with each oxygen covalently bonded to 2 silicon atoms
- high melting point
- does not conduct electricity
- insoluble in water
Properties of graphite
- Each C atom is joined to three others to form hexagonal layers
- has a high melting point
- is insoluble in water
- it is soft
- it conducts electricity
Why is graphite a conductor and soft
- The spare electron becomes delocalised between the layers
- These mobile electrons enable graphite to conduct electricity
- The graphite layers can slide over one another, making graphite soft and slippery
Allotropes
Molecules with different structural arrangements with different properties
- diamond, graphite (C)
Types of intermolecular forces
- Dispersion Forces
- Dipole / dipole attraction
- Hydrogen Bonding
Dispersion forces
Between all substances due to the constant movement of electrons.This gives rise to electrostatic forces of attraction.
The electrons around a covalent bond are constantly moving and will form temporary dipole attraction
• very weak
Dipole-Dipole forces
When there is a difference in electronegativity between two atoms in a molecule, a permanent dipole is created
Hydrogen bond
This is a dipole-dipole attraction that occurs between molecules with Hydrogen bonded to a “NOF’ and attracted to a “NOF”
Polar bond
A bond resulting from an uneven sharing of electrons between two
atoms.
Polar molecule
Polar molecules arise when the intramolecular bonds are polar.
If the molecule is asymetrical then a polar molecule will be formed since there is an overall uneven distribution of charge.
