2 Bonding, Structure and the Properties of Matter Flashcards
Metals lose electrons and form ________ ions.
__________ gain electrons and form ________ ions.
1) positive
2) Non-metals
3) negative
Ionic bonds occur between…
…positive and negative ions.
Ionic bonding
The transfer of electrons from metal atoms to non-metal atoms. The electrons are completely given away.
Sodium forms an ionic compound with chlorine. Describe what happens when two atoms of sodium react with one molecule of chlorine.
Draw a dot cross diagram to help you.
Na = group 1, so 1 electron on its outer shell; two Na atoms so 2 electrons, 1 electron needs to be removed from each sodium (2 electrons)
Cl = group 7, so 7 electrons on its outer shell, Cl molecule = Cl2, so two molecules; 1 electron is needed for each chlorine (2 electrons)
↪Na belongs to group 1, so it has 1 e⁻ on its outer shell. Cl belongs to group 7, so it has 7 e⁻ on its outer shell.
Na needs to lose 1 e⁻ whilst Cl needs to gain 1. Cl has two atoms of Cl in it (Cl2). Each Na atom transfers 1 e⁻ to one of the Cl atoms. All four atoms now have 8 e⁻ in their outer shell. The atoms become ions: Na⁺ and Cl⁻. The compound formed is sodium chloride, NaCl.
2Na + Cl2 → 2NaCl
[Na]⁺ [Cl]⁻
Ionic bond
The attraction between oppositely charged ions.
Empirical Formula
The simplest expression of the ratio of ions.
E.g. C2H6: CH3 or C2H4: CH2
Covalent bond
A shared pair of electrons between atoms.
Covalent bonding
- Happen between non-metals
- Happen in non-metal compounds
- The electrons are shared (co means sharing)
Simple and Covalent Molecules
- Substances which contain simple molecules are usually liquids or gases
- Have low melting/boiling points because of weak intermolecular forces
- Intermolecular forces are very weak compared to the strength of covalent bonds in the molecules themselves
- Weak forces of attraction are easy to overcome, hence low melting/boiling points in simple molecular substances
Intermolecular force
Forces of attraction between molecules.
Why can’t covalent molecules conduct electricity?
Because they do not have an overall charge.
Polymers
- Consist of 𝘃𝗲𝗿𝘆 large molecules
- Have 1000s and 1000s of atoms
- The atoms within polymer molecules are linked together by strong covalent bonds
- The intermolecular forces between the large polymer molecules are 𝙧𝙚𝙡𝙖𝙩𝙞𝙫𝙚𝙡𝙮 𝙨𝙩𝙧𝙤𝙣𝙜 which is why polymers are solid at room temperature
- But the forces are weak enough to allow the chains to slide over each other which makes the substance flexible
Give three examples of giant covalent structures and draw a diagram for each.
- Diamond
- Graphite
- Silicon dioxide (silica)
Allotrope
A form of an element.
E.g. diamond and graphite are both forms of carbon. Graphene, fullerenes and nanotubes are also other forms of carbon allotropes.
Metallic bond
The attraction between positive ions and delocalised electrons.
Metallic bonding occurs in…
- Metallic elements
* Alloys (e.g. stainless steel)
Alloy
A mixture of two or more elements, at least one of which is a metal. Usually, the alloy is stronger and 𝗵𝗮𝗿𝗱𝗲𝗿 than the pure metal. E.g.
Bronze = copper + tin
Brass = copper + zinc
Steel = iron + carbon
In alloys, the added element ________ the regular arrangement of _____ atoms so the ______ do not _____ ____ ____ _____ so easily.
1) disturbs
2) metal atoms
3) layers
4) slide over each other
Alloys are harder because…
…the regular layer structure has been disrupted.
Diamond
- Carbon atoms
- Covalent bonds
- Giant structure
- Each carbon makes 4 bonds
- 3D
- Can’t conduct electricity because it has no charged electrons
- Hard because it has a giant covalent structure, its 3D and it has strong covalent bonds
Graphite
- Carbon atoms
- Covalent bonds
- Giant structure
- Each carbon makes 3 bonds
- 2D
- Weak forces of attraction between layers
- Has delocalised electrons that move between layers
- Can conduct electricity because it has delocalised electrons
- Soft layers can slide because of weak forces of attraction
Solid - Liquid - Gas
→ increasing in kinetic energy of particles
The energy required to change state depends on the 𝘀𝘁𝗿𝗲𝗻𝗴𝘁𝗵 𝗼𝗳 𝗳𝗼𝗿𝗰𝗲𝘀 holding the particles together…
Stronger forces = Higher melting/boiling point
Describe what happens when a substance changes state.
- The particles stay the same
- Their arrangement changes
- The way they move changes
In simple molecules, why are melting and boiling points low?
- Weak intermolecular forces of attraction
* Therefore, little energy is needed to overcome these forces
Why can graphite conduct electricity but diamond cannot?
- Graphite has delocalised electrons which allow it to conduct electricity
- Diamond has no charged particles so it can’t conduct electricity
Why do people disagree with the use of silver nanoparticles?
- Nanoparticles are so small they could get into and damage human cells (cross blood barrier)
- They could cause problems in the environment
𝗶𝗼𝗻𝗶𝗰 𝗰𝗼𝗺𝗽𝗼𝘂𝗻𝗱 𝗰𝘂𝗯𝗲 𝗱𝗶𝗮𝗴𝗿𝗮𝗺
How is this model useful and how is it misleading?
- Useful because it shows how many bonds each ion makes
* Misleading: Makes us believe that the substance has a cubic structure
State and explain how the properties of solid salt change when it dissolves in water.
- As a solid, the ions are in fixed positions, so they cannot move, therefore they can’t conduct electricity
- When dissolved, the ions are now free to move and carry a charge, so they can conduct electricty
