Bonding Flashcards
What does ionic bonding occur between?
Metals and non-metals
Describe the movement of electrons in ionic bonding:
Electrons are transferred from metal atoms to non-metal atoms
What is ionic bonding a result of?
An electrostatic attraction between oppositely charged ions. This attraction extends throughout the compound
What structure do ionic compounds always exist as?
Ionic lattices
Why are ionic compounds always solids at room temperature and why do they have high melting points?
They are always solid at room temperature. They have giant structures and therefore high melting temperatures.
This is because in order to melt an ionic compound, energy must be supplied to break up the lattice of ions.
Describe the conductivity of ionic compounds:
Ionic compounds conduct electricity when molten or dissolved in water. This is because the ions that carry the current are free to move in the liquid state but not the solid state
Why are ionic compounds brittle and easily shattered?
Because they form a lattice of alternating positive and negative ions. A blow may move the ions and produce contact between ions with like charges
What does a covalent bond form between?
A pair of non-metal atoms
What is a covalent bond?
A covalent bond is a shared pair of electrons
What is a small group of covalently bonded atoms called?
A molecule
How does sharing electrons hold atoms together?
Atoms with covalent bonds are held together by electrostatic attraction between the nuclei and the shared electrons. This takes place within the molecule
In a double bond, how many electrons are shared?
4
Why do substances composed of molecules have low melting temperatures?
Because the strong covalent bonds are only between the atoms within the molecule. There is only weak attraction between the molecules so the molecules do not need much energy to move apart from each other
Why are covalently bonded molecules poor electrical conductors?
Because the molecules are neutral overall. This means that there are no charged particles to carry the current
What is a coordinate/ dative covalent bond?
A bond where one atom provides both of the electrons
How do coordinate bonds compare with covalent bonds?
They have exactly the same length and strength as ordinary covalent bonds between the same pair of atoms
What is a simple picture of metallic bonding?
Metals consist of a lattice of positive ions existing in a ‘sea’ of outer electrons which are delocalised (they’re not tied to a particular atom)
What does the number of delocalised electrons depend on?
How many electrons have been lost by each metal atom
Why do metals have giant structures?
Because the metallic bonding spreads throughout
Why are metals good conductors of electricity?
Because the delocalised electrons can move throughout the metal structure
Why are metals good conductors of heat?
Because of the sea of delocalised electrons as well as energy being spread by increasingly vigorous vibrations of the closely packed ions
What does the strength of the metallic bond depend on?
- the charge of 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 the ion - the smaller the ion, the closer the electrons are the positive nucleus and the stronger the bond
Why are metals generally strong?
Because the delocalised electrons extend throughout the solid so there are no individual bonds to break
Why are metals malleable and ductile?
Because after a small distortion, each metal ion is still in exactly the same environment as before so the new shape is retained
Why do metals have high melting and boiling points?
Because they have giant structures. There is a strong attraction between metal ions and the delocalised sea of electrons. This makes the atoms difficult to separate
What is electronegativity?
Electronegativity is the power of an atom to attract the electron density in a covalent bond towards itself
What scale is used to measure electronegativity?
The Pauling scale
Why do the noble gases not have an electronegative value?
Because, in general, they do not form covalent bonds
What three things does electronegativity depend 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 up a group?
Electronegativity increases (the atoms get smaller) and there is less shielding by electrons in inner shells
What is the trend in electronegativity across a period?
Electronegativity increases across a period because nuclear charge increases, the number of inner main levels remain the same and the atoms become smaller
What is polarity?
It is about the unequal sharing of the electrons between atoms that are bonded together covalently. It is a property of the bond
Why are electrons in covalent bonds between two atoms that are the same shared out equally?
Because both atoms have exactly the same electronegativity and the bond is completely non-polar
What are polar covalent bonds?
Covalent bonds where one end of the bond is more negative than the other because of an unequal distribution of electrons
Where do van der Waals forces occur?
They act between all atoms and molecules
What is the strongest type of intermolecular force?
Hydrogen bonding
What is a dipole moment?
The effect of the polarity of all the bonds in the molecule
