Bonding Flashcards
Properties of ionically bonded compounds
Ionic compounds are always solids at room temperature. They have giant structures and therefore high melting temperatures. This is because , energy must be supplied to break up the lattice of ions.
Ionic compounds conduct electricity when molten or dissolved in water (aqueous) but not when solid. This is because the ions that carry the current are free to move in the liquid state but are not free in the solid state
How does sharing electrons in a covalent bond hold it tigether
Atoms with covalent bonds are held together by the electrostatic attraction between the nuclei and the shared electrons. This takes place within the molecule. The simplest example is hydrogen. The hydrogen molecule consists of two protons held together by a pair of electrons. These electrostatic forces just balance when the nucici are a particular distance apart.
Double covalent bond
In a double bond, four electrons are shared.
Properties of substances with molecular structures
Substances composed of molecules are gases, liquids, or solids with low melting temperatures. This is because the strong covalent bonds are only betwen the atons within the molecules. There is only weak attraction between the molecules so the molecules do not need much energy to move apart from each other.
They are poor conductors of electricity because the molecules are neutral overall. This means that there are no charged particles to carry the current.
Il they dissolve in water, and remain as molecules, the solutions do not conduct electricity. Again, this is because there are no charged particles.
Dative bonding
A single covalent bond consists of a pair of electrons shared between two atoms. In most covalent bonds, each atom provides one of the electrons.
But, in some bonds, one atom provides both the electrons.
the atom that accepts the electron pair is an atom that does not have a filled outer main level of electrons - the atom is electron-deficient
• the atom that is donating the electrons has a pair of electrons that is not being used in a bond, called a lone pair.
More dative bonds
Dative bonds have exactly the same strength and length as ordinary covalent bonds between the same pair of atoms.
Metallic bonding
The atoms in a metal element cannot transfer electrons unless there is a non-metal atom present to receive them. In a metal element, the outer main levels of the atoms merge.
The outer electrons are no longer associated with any one particular atom. A picture is that metals consist of a lattice of positive ions existing in a ‘sea’ of outer electrons. These electrons are delocalised. This means that they are not tied to a particular atom. The positive ions tend to repel one another and this is balanced by the electrostatic attraction of these positive ions for the negatively charged ‘sea” of delocalised electrons.
More metallic bonding
• The number of delocalised electrons depends on how many electrons have been lost by each metal atom.
• The metallic bonding spreads throughout so metals have giant structures
Properties of metals
Metals are good conductors of electricity and heat
The delocalised electrons that can move throughout the structure explain why metals are such good conductors of cleciricty.
Metals are also good conductors of heat - they have high thermal conductivities. The sea of electrons is partly responsible for this property, with energy also spread by increasingly vigorous vibrations of the closely packed ions.
Strength of metals
In general, the strength of any metallic bond depends on :
• the charge on the ion - the greater the charge on the ion, the greater the number of delocalised electrons and the stronger the electrostatic attraction between the positive ions and the electrons.
• the size of ion - the smaller the ion, the closer the electrons are to the positive nucleus and the stronger the bond.
Malleable metals
Metals are malleable and ductile . After a small distortion, each metal ion is still in exactly the same environment as before so the new shape is retained,
Metals high melting points
Metals generally have high melting and boiling points because they have giant structures. There is strong attraction between metal ions and the delocalised sea of electrons. This makes the atoms dillicult to separate.
