structure and bonding

Metal type of bonding and structure

Metallic, giant lattice

Non metal type of bonding and structure

Covalent, simple molecular

Compounds of metals with non metals type of bonding and structure

Ionic, giant lattice

Metallic structure

LAYERS of positively charged metals IONS, closely packed together in a sea of DELOCALISED ELECTRONS

Metallic bonding

Strong ELECTROSTATIC ATTRACTION between all the (positive) IONS and the delocalised (negative) ELECTRONS

Why can metals conduct electricity?

The DELOCALISED ELECTRONS are free to MOVE / FLOW through the structure.

Why are metals malleable?

The LAYERS OF IONS (/metal atoms) are able to SLIDE OVER EACH OTHER.

Why do metals have high melting points?

There is very STRONG ELECTROSTATIC ATTRACTION between the ions and the (delocalised) electrons which TAKES A LOT OF ENERGY TO OVERCOME.

1)    IONIC COMPOUNDS

THE STRUCTURE

GIANT LATTICE OF OPPOSITELY CHARGED IONS.

IONIC BONDING

There is strong ELECTROSTATIC ATTRACTION between the OPPOSITELY CHARGED IONS.

Why do ionic compounds have high melting points?

The STRONG ELECTROSTATIC ATTRACTION between the OPPOSITELY CHARGED IONS TAKES A LOT OF ENERGY TO OVERCOME.

Why do some ionic compounds have higher melting points than others?

The HIGHER THE CHARGE ON THE IONS the STRONGER THE ATTRACTION between them, so the higher the melting point will be.

Why can ionic compounds conduct electricity when they are melted or dissolved in water (electrolysis)?

The IONS are ABLE TO MOVE AROUND when the compound is in the liquid state.  The positive ions move to the negative electrode and the negative ions move to the positive electrode.

 

Why can’t ionic compounds conduct electricity when they are solid?

The IONS are NOT ABLE TO MOVE AROUND when the compound is in the solid state.  They are in fixed positions in the crystal lattice (can only vibrate).

1)    SIMPLE MOLECULAR SUBSTANCES

THE STRUCTURE

SMALL MOLECULES.

THE BONDING

·      COVALENT BONDS.  Covalent bonds are strong.

·      A covalent bond is A PAIR OF ELECTRONS SHARED BETWEEN TWO ATOMS.

Why do simple molecular substances have low melting and boiling points?

There are only WEAK INTERMOLECULAR FORCES between the separate molecules.  These TAKE ONLY A LITTLE ENERGY TO OVERCOME.

Why can’t molecular compounds conduct electricity at all?

There are NO CHARGED PARTICLES ABLE TO MOVE AROUND.  (All the electrons are tied up in the covalent bonds and there are no charged ions present.)

1)    GIANT COVALENT SUBSTANCES (DIAMOND & GRAPHITE)

THE STRUCTURE

GIANT LATTICE OF ATOMS

THE BONDING

COVALENT BONDS

Why do giant covalent substances have high melting points?

There are MANY STRONG COVALENT BONDS between all the atoms.  These TAKE  A LOT OF ENERGY TO BREAK.

Why is diamond very hard?Why is diamond very hard?

There are VERY STRONG COVALENT BONDS between all the carbon atoms.  There are no weak links. 

Why is graphite soft and greasy?

The carbon atoms in graphite are in LAYERS.  There are ONLY WEAK FORCES / ATTRACTIONS BETWEEN THE LAYERS.  The layers of carbon atoms can SLIDE OVER EACH OTHER easily.  This makes graphite useful as a lubricant

Why can’t diamond conduct electricity?

There are NO CHARGED PARTICLES ABLE TO MOVE AROUND.

Why can graphite conduct electricity?

There are DELOCALISED ELECTRONS in graphite and these are free to MOVE / FLOW through the structure.