Bonds, Structure and Properties of Matter Flashcards
what is an ion?
An ion is an atom or group of atoms with a positive or negative
charge. Ions form when atoms lose or gain electrons to obtain a full outer shell
metal atoms … electrons to form …
metal atoms lose electrons to form positively charged ions
non-metal atoms … electrons to form …
non-metal atoms gain electrons to become negatively charged ions
where do metals lose their electrons from when they form ions?
their outer shell
what do ions have the electronic structure of?
They have the electronic structure of noble gases with a full outer shell
How are positive ions positive?
They lose electrons so there are more protons than electrons, giving the atom a positive overall charge
How are negative ions negative?
They gain electrons so they have more electrons than protons, giving the atom a negative overall charge
what to remember for groups 1, 2 and 3?
the number of electrons lost is the same number as the group number
(e.g. Sodium is in group 1, so it loses 1 electron)
what to remember for groups 6 and 7?
For elements in groups 6 and 7, the charge on the ion is equal to (8 minus group number).
example question - Iodine is in group 7. What is the charge on its ions, and is the charge positive or negative?
The charge is negative, since iodine is a non-metal. The charge on the ion is (8 - 7) = 1.
When does ionic bonding form?
Ionic bonding forms between two atoms when an electron is transferred from one atom to the other, forming a positive-negative ion pair - with strong electrostatic forces between them.
What is a dot and cross diagram?
A dot and cross diagram models the transfer of electrons from metal
atoms to non-metal atoms. The electrons from one atom are shown as dots, and the electrons from the other atom are shown as crosses.
What is an ionic lattice?
The regular arrangement of ions in an ionic substance.
How do ionic lattices occur?
The lattice is formed because the ions attract each other and form a regular pattern with oppositely charged ions next to each other.
Why do solid ionic compounds form crystals with regular shapes?
Since ionic lattices are giant (one grain of salt could contain 1.2 × 10^18 (1,200,000,000,000,000,000 ions)), the lattice continues in 3 dimensions
What is an ionic lattice held together by?
An ionic lattice is held together by strong electrostatic forces of attraction between the oppositely charged ions. The forces act in all directions in the lattice.
pros and cons of the 2D model
the two-dimensional space-filling model clearly shows the arrangement of ions in one layer, but it does not show how the next layer of ions is arranged
why is the 3D model misleading?
the three-dimensional model is misleading because it shows lots of free space between the ions, which there isn’t
pros and cons of 3D ball and stick model
the three-dimensional ball and stick model shows the arrangement of ions in a larger section of the crystal, but using sticks for bonds is misleading because the forces of attraction between ions actually act in all directions
what state are ionic compounds in at room temperature?
solid
why do ionic compounds have a high melting and boiling point?
The more energy needed, the higher the melting point or boiling point. Since the electrostatic forces of attraction between oppositely charged ions are strong, their melting and boiling points are high.
when can ionic compounds conduct electricity?
An ionic compound can conduct electricity when:
it has melted to form a liquid, or it has dissolved in water to form an
aqueous solution
Both these processes allow ions to move from place to place. Ionic compounds cannot conduct electricity in the solid state because their ions are held in fixed positions and cannot move.
what does the strength of the ionic bonds depend on
The strength of the ionic bonds depends on the charge on the ions. Ions with higher charge will have stronger forces between them, so will need more energy in order to overcome these forces.
when is a covalent bond formed?
A covalent bond is formed when two atoms share a pair of electrons.
what type of elements are covalent bonds formed in?
Covalent bonding occurs in most non-metal elements, and in compounds formed between non-metals.
what do most covalently bonded substances consist of?
Most covalently bonded substances consist of small molecules
what is a molecule?
A molecule is a group of two or more atoms joined together by covalent bonds.
what do substances made up of ions NOT form?
Substances that are made up of ions do not form molecules.
dot and cross diagrams for covalent bonds look like:
- the outer shell of each atom is drawn as a circle
- circles overlap where there is a covalent bond
- electrons from one atom are drawn as dots, and electrons from
another atom as crosses
what is structural formulae?
A structural formula shows the bonds between the atoms in a molecule. In these formulae:
- each atom is shown by its chemical symbol
- each covalent bond is shown as a straight line
What do three-dimensional structures show?
These models show how the atoms and bonds are arranged in space. The diagram shows a ball and stick model of ammonia.
pros and cons of dot and cross diagrams representing molecules
A dot and cross diagram shows the pairs of outer electrons, and which atoms they have come from. It does not show how the atoms are arranged in space.
pros and cons of a structural formula representing molecules
The structural formula shows the bonds between the atoms, but it does not show which atoms the electrons in the bonds have come from.
interpret the dot and cross diagram to find the formula, name and structural formula of the molecule
interpret the formula to find the dot and cross diagram, name and structural formula of the molecule
what is a double or triple covalent bond?
a bond consisting of 2 or 3 shared pairs of electrons
from this dot and cross diagram, find the structural formula
from this dot and cross diagram, find the structural formula
A substance with small molecules has ….. covalent bonds
A substance with small molecules has strong
covalent bonds, that keep the atoms together in molecules
There are ….. forces between molecules and their neighbours
There are weak forces between molecules and their neighbours. In short, there are weak intermolecular forces
Why do most simple molecules have low melting and boiling points
Intermolecular forces are much weaker than the strong covalent
bonds in molecules. When small molecular substances melt or boil, it is these weak forces that are overcome. The covalent bonds are not broken. Relatively little energy is needed to overcome the intermolecular forces, so small molecular substances have low melting and boiling points.
In general, the …. the molecule, the …. the intermolecular forces, so …
In general, the bigger the molecule, the stronger the intermolecular forces, so the higher the melting and boiling points.
Why can’t small molecules conduct electricity?
Small molecules have no overall electric charge, so they cannot conduct electricity, even when liquid or dissolved in water.
what are giant covalent subtsances?
substances that contain many atoms joined by covalent bonds
Where is silicon dioxide found?
Silicon dioxide (often called silica) is the main compound found in sand. It is an example of a substance with a giant covalent structure.
Which elements does silica contain
Silica contains lots of silicon and oxygen atoms
How is silicon dioxide (silica) a giant covalent structure?
All the atoms in its structure are linked to each other by strong covalent bonds. The atoms are joined to each other in a regular arrangement, forming a giant covalent structure. There is no set number of atoms joined together in this type of structure
Which giant covalent structure is this?
Silicon dioxide (silica)
What state are substances with giant covalent structures at in room temperature
Substances with giant covalent structures are solids at room temperature.
Why do substances with giant covalent structures have high melting and boiling points?
This is because large amounts of energy are needed to overcome their strong covalent bonds to make them melt or boil.
Why can most substances with giant covalent structures not conduct electricity.
Most substances with giant covalent structures have no charged particles that are free to move, meaning they can’t conduct electricity.
State three properties that are typical of substances with giant covalent structures.
They have high boiling points, high melting points and they cannot conduct electricity.
Which giant covalent structure can conduct electricity?
Graphite - a form of carbon
