3. Bonding Flashcards
Nobel gases…
Have full outer main levels of electrons and are very unreactive
Which electrons do the bonds between atoms always involve?
The outer electrons
Name the three strong chemical bonds
- Ionic
- Covalent
- Metallic
How many electrons do metals have in their outer main levels?
One, two or three electrons.
Metals have either one, two or three electrons in their outer shells. What is the easiest way for them to attain the electron structure of a nobel gas?
To loose their outer electrons.
Which type of bonding occurs between metals and non-metals?
Ionic bonding
Electrons are transferred from metal atoms to non-metal atoms
Positive and negative ions are formed
The positive and negative ions formed in an ionic bond are attracted to each other by which force?
Electrostatic force
In ionic bonding how far does the electrostatic force extend?
The attraction extends throughout the compound. Every positive ion attracts every negative ion and vice versa.
What repulsive force exists in an ionic bond?
The repulsive force between all the ions of the same charge.
What is the structure in which all ionic compounds exist? How are the forces distributed in this?
A lattice
The attractive forces and the repulsive forces are balanced
What is the state of an ionic lattice at room temperature?
Solid, they have high melting temperatures because of their giant structures.
To melt a lattice of ions, what would you have to do?
Supply enough energy to break up the lattice of ions.
I.e break the electromagnetic forces of attraction.
Do ionic compounds conduct electricity?
Ionic compounds conduct electricity when molten or dissolved in water (aqueous) but not when solid.
Why do ionic compounds conduct when they are molten/aqueous but not when they are solid?
The ions that carry the current are free to move in the liquid state but they are not free in the solid state.
Ionic compounds are…
Brittle and shatter easily when given a sharp blow.
Why do ionic compounds shatter when given a sharp blow?
Because they form a lattice of alternating positive and negative ions, a blow may move e ions and produce contact between ions with like charges.
Do non-metals need to loose or receive electrons to gain electron structures of nobel gases?
Non-metal atoms need to receive electrons to fill the spaces in their outer shells.
Which type of bond is formed between a pair of non-metals?
A covalent bond
What is a covalent bond?
A shared pair of electrons
What is a small group of covalently bonded molecules called?
A molecule
How are covalent molecules neutral?
Because no electrons have been transferred from one atom to another
How does sharing electrons hold atoms together in covalent bonds?
Atoms with covalent bonds are held together by the electrostatic attraction between the nuclei and the shared electrons.
(The molecules are not strongly attracted to each other).
What kind of melting point do substances composed of molecules have?
Substances composed of molecules are gases, liquids or solids with low melting points
Why do substances composed of molecules have low melting points?
Because the strong covalent bonds are only between the atoms within the molecules. There is only weak attraction between the molecules which do not take much energy to overcome.
Are substances composed of molecules good conductors?
They are poor conductors of electricity because the molecules are neutral overall. There are no changed particles to carry the current. (Even when aqueous).
What is co-ordinate bonding/dative covalent bonding?
When one atom provides both electrons in a covalent bond.
What do we call the atom that accepts the electron pair in a co-ordinate bond?
Electron-deficient
What are two spare electrons on an atom not being used in a bond called?
A lone pair
Co-ordinate covalent bonds are represented by what?
An arrow pointing towards the atom which is accepting the electron pair.
A molecule with a co-ordinate bond (and other covalent bonds) has bonds of what strength?
All the bonds have exactly the same strength and length. The molecule is symmetrical.m
What is electronegativity?
The power of an atom to attract the electrons in a covalent bond.
What is the word used to describe the way the negative change is distributed in a molecule?
The electron density
Which scale is used as a measure of electronegativity?
The Pauling scale
What numbers does the Pauling scale range?
0-4 (4 has the greatest electronegativity)
Which group of elements have no number on the Pauling scale?
The nobel gases, because they do not form covalent bonds
List three things electronegativity depends on?
- The nuclear charge
- The distance between the nucleus and the outer shell electrons
- The shielding of the nuclear charge by electrons in inner shells.
What is the trend in electronegativity as we go up a group in the periodic table?
It increases as there is less shielding by electrons in inner shells.
What is the trend in electronegativity as we go across a period in the periodic table?
The electronegativity increases. The nuclear charge increases, the number of inner main levels stays the same and the atoms become smaller.
N the periodic table where are the most electronegative atoms found?
At the top right-hand corner