Bonding, structure and the properties of matter

Why do atoms bond together?

To end up with a more stable arrangement of electrons, usually from gaining a full outer shell of electrons

How to atoms form ionic bonds?

-In an atom there are attractive forces between the nucleus and the electrons

-When two atoms approach, nucleus begins to attract electrons in the other atom too. This pulls the atoms closer

-Metal atoms have 1-3 outer electrons. Compared to non metals, they are weakly held by the nucleus

-Nucleus in non-metal atom attracts the outer electrons in the metal atom so strongly that there is a transfer of electrons from the metal to the non metal atom

-Metal atom ends up positively charged with complete outer shell. Now positive ion

-Non-metal atom ends up negatively charged with complete outer shell. Now negative ion

Which atoms are ionic bonds formed between?

Metals and non metals

How do atoms form covalent bonds?

-In an atom, there are attractive forces between the nucleus and electrons

-When two atoms approach, the nucleus begins to attract electrons in the in the other atoms. This pulls atoms closer

-As nuclei continue to pull each other's electrons, the outer electron shells overlap

-Eventually, repulsive forces between the nuclei and between the electrons in each atom prevent the atoms from getting any closer

-Left with two atoms joined together and electrons being shared where the outer shells have over-lapped

How are electrons arranged in metallic bonds?

-In metals the outer electrons arranged not tightly bound to the nucleus

-The outer electrons can drift from atom to another. They are delocalised

Why do metals conduct electricity?

The delocalised electrons can move throught the structure, allowing them to carry the electric charge

Why are metals malleable?

Because the outer electrons are delocalised, the layers of atoms can slide over each other without breaking their bonds

What are the properties of giant ionic structures?

-High melting points

-Hard crystals

-Do not conduct electricity in solid state but do when molten or dissolved in water

Why do ionic structures only conduct electricity when molten or dissolved?

They are made up of charged particles but they are closely packed together in their solid state. When molten or dissolved, the ions can move freely, allowing them to carry the electric charge

Why do giant ionic structures have a high melting point?

There are strong electrostatic forces between the oppositely charged ions. Therefore it takes a lot of energy to break these bonds.

What are the properties of giant covalent structures?

-High melting points

-Hard crystals (except graphite)

-don’t conduct electricity (except graphite)

What is the evidence that giant covalent structures are made of atoms?

-Don’t conduct electricity so made of uncharged particles

-Not made up of molecules because bonds between molecules are weak

Why do giant covalent structures have high melting points?

There are strong covalent bonds between the atoms. Therefore it takes a lot of energy to break these bonds.

What are the properties of simple molecular/simple covalent structures?

-Don’t conduct electricity

-Low melting points

-Low boiling points

Why do simple molecular/covalent structures have low boiling points?

Although the atoms are held together by strong covalent bonds, there are only weak (intermolecular) forces between the molecules. When a simple covalent substance boils or melts, it is the molecules that separate from each other (not the atoms)

What are the properties of metals?

-Good conductors of heat and electricity

-Malleable (can be hammered into any shape)

-Ductile (can be drawn into a wire)

-Shiny

What is an alloy?

A mixture of two metals

Why ate metals ductile and malleable?

The bonding in a giant metallic lattice cannot be broken. When a metal is hammered or drawn into a wire, the metal ions slide over each other to new lattice positions. The delocalised electrons still continue to hols the lattice together

Why are alloys often stronger and harder than pure metal?

When there are different sized atoms within each layer, it’s harder for the layers of atoms to slide over each other. Therefore alloys are often more rigid, harder and stronger.

Why do most metals have high melting points?

They have a giant metallic structure. There are strong electrostatic attractions between the positive metal ions and the delocalised electrons

What are the allotropes of carbon?

-Diamond

-Graphite

-Fullerenes

What are the properties of diamond?

-Hard

-Has high melting point (3550⁰C)

-Cannot conduct electricity because there are no ions or free electrons to carry charge

What structure does diamond have?

Giant covalent - eash carbon atom is held in place by 4 strong covalent bonds

What is the structure of graphite?

Made of flat sheets of carbon atoms. Each carbon atom forms strong covalent bonds to three other carbon atoms. This gives rings of six atoms. The rings join to make flat sheets that lie on top of each other, held together by weak forces

Why does graphite conduct electricity?

Since carbon only bonds to 3 other atoms there is one free outer electron (carbon has 4 outer electrons). The free electron is delocalised so it can carry the charge

What are the properties of graphite?

-High melting point because atoms held together by strong covalent bonds which require a lot of energy to break

-Soft and slippery because atoms can slide over each other easily - no covalent bonds between the layers just weak forces

-Conducts electricity

What is graphene?

A single layer of graphite

What are the properties of graphene?

-Thinnest material on earth and transparent

-Ultra light yet very tough

-200 times stronger than steel but incredibly flexible

-Conductor

-very good barrier - not even helium can pass through it

What structure does graphene have?

Giant covalent

Why does graphene have a high melting point?

Strong covalent bonds between the carbon atoms which require a lot of energy to break

Why does graphene conduct electricity?

Each carbon atom forms three covalent bonds to three other carbon atoms, leaving one delocalised electron

What is a carbon nanotube?

Graphene folded into a cylinder. They are very strong

What shape are the molecules in buckminsterfullerene and how many carbon atoms does it contain?

Molecules are spherical and contain 60 carbon atoms in one molecule

What is the bonding in graphene?

Each atom forms three covalent bonds to three other carbon atoms. There is one electron spare in each carbon atom's oter shell, which is delocalised

What is the melting point of buckminsterfullerene C60?

Not as high as diamond or graphite because it is made of molecules and there are no strong chemical bonds between these molecules. There are just intermolecular forces which are much weaker than covalent bonds. Therefore, it doesn't take as much energy to break the intermolecular forces in buckminsterfullerene as it does to break the strong covalent bonds in graphite

What are models used for?

To model the physical and chemical properties of matter in an effort to explain why matter behaves in certain ways