Chemistry topic 2 Flashcards
(33 cards)
How are ions made when electrons are transferred?
Ions are charged particles which can be single or groups of atoms.
When they gain or lose electrons to form ions, all they’re trying to do is get a full outer shell and become stable.
When metals form ions, they lose electrons to form positive ions.
When non metals form ions, they gain electrons to form negative ions.
The number of electrons lost or gained is the same charge of the ion.
Why are groups 1, 2, 6 and 7 most likely to form ions?
Groups 1 and 2 elements are metals and they lose electrons to form positive ions (cations). Group 6 and 7 are non metals and gain electrons to form negative ions (anions).
You don’t have to remember which ions most elements form, just look at the periodic table. Element in the same group all have the same number of outer electrons, so they have to lose of gain the same number to get a full outer shell (meaning they form ions with the same charge).
What is ionic bonding?
When a metal and a non metal react together, the metal atom loses electrons to form a positively charged and the non metals gain electrons to form a negatively charged ion. The oppositely charged ions are strongly attracted to each other by electrostatic forces. This attraction is called an ionic bond.
PRACTICE DOT AND CROSS DIAGRAMS…..
Explain why ionic compounds have a regular lattice structure:
Ionic compounds have a structure called a giant ionic lattice. The ions form a closely packed regular lattice arrangement and there are strong electrostatic forces of attraction between oppositely charged ions, in all directions of the lattice.
LOOK AT THE DIAGRAMS IN THE TEXTBOOK.
What are the properties of ionic compounds?
- high melting and boiling points due to many string bonds between the ions, it takes a lot of energy to overcome this.
- when they’re solid, the ions are held in place so the compounds can’t conduct, but when they melt, the ions are free to move and they’ll carry electric current.
- some ionic compounds dissolve in water, the ions separate and are free to move in the solution, so they’ll carry the electric current.
How do you find the formula of an ionic compound?
YOU LOOK AT THE CHARGES
you might have to work out the empirical formula of an ionic compound from each diagram of the compound.
If it’s a dot and cross diagram, count up the amount of atoms per element.
If you’re given a 3d diagram of the ionic lattice, use it to work out the ions in the compound.
You’ll then have to balance the charges of the ions so the overall charge of the compound is zero.
What are covalent bonds?
- When non-metal atoms bond together, they share pairs of electrons to create covalent bonds.
- The positively charged nuclei are attracted to the shared pair of electrons by electrostatic forces, making them very strong.
- atoms only share electrons in their outer shell (highest energy level).
- each single covalent bond provides one extra shared electron for each atom.
- each bond means the atoms have a full outer shell, making them stable (like a noble gas).
- these bonds happen in compounds of non metals and in non metal elements.
What are the 3 different ways to draw covalent bonds?
- dot and cross diagrams
- molecular (visual) formula
- simple formula (letters)
What is a simple molecular substance?
Give some examples…
Made up of molecules containing a few atoms joined together by covalent bonds.
Eg. Hydrogen, oxygen, methane, chlorine, nitrogen, water, hydrogen chloride…
What are the properties of simple molecular substances?
- usually the product of a covalent bond
- the atoms are held together by strong covalent bonds, but the forces of attractions are weak
- To melt or boil, you only need to break these feeble intermolecular forces, and not the covalent bonds. (The bpt are very low)
- most molecular substances are gases or liquids at room temperature.
- as molecules get bigger, the strength of the intermolecular forces increases, so more energy is needed to break them, so melting and boiling points increase.
- molecular compounds do not conduct electricity, simply because they aren’t charged, so there are no free electrons or ions.
What is a polymer?
In a polymer, lots of small units are linked together to form a long molecule that has repeating sections.
All the atoms in a polymer are joined by strong covalent bonds.
Instead of drawing out a whole long, polymer molecule you can draw the shortest repeating section called the repeating unit.
To find the molecular formula of a polymer, write down the molecular formula of the repeating unit in brackets and put an N outside. So for polythene, the molecular formula of the polymer is (c4h4)n.
The intermolecular forces between the polymer molecules are larger than between simple covalent molecules.
So more energy is needed to break them, meaning they are solid at room temperature. The intermolecular forces are still weaker than ionic or covalent bonds, so they generally have lower boiling points, than ionic or giant molecular compounds.
What is a giant covalent structure?
A MACROMOLECULE!
enjoyment covalent structures for the atoms are bonded together by strong covalent bonds, meaning they have a very high melting and boiling point as lots of energy is needed to break these bonds. They don’t contain charged particles, don’t conduct electricity, not even when Molten. diamond and graphite which are both made from carbon atoms only and silicon dioxide.
What is diamond?
Describe the structure
Diamond has a giant covalent structure, made up of carbon atoms to teach form for covalent bonds, making it really hard. The strong covalent bonds take a lot of energy to break and give diamond a very high melting point. It doesn’t conduct electricity because it has no free electrons or ions.
What is graphite?
Describe the structure
In graphite each carbon atom, only forms three covalent bonds, creating sheets of carbon atoms arranged in hexagons. There aren’t any covalent bonds between the layers, meaning that only how to get a weekly so free to move over each other. This makes graphite soft and slippery so it’s ideal as a lubricating material.N it has a high melting point as the covalent bonds in the layers need loads of energy to break. Only three out of each of carbon is four outer electrons are used in bonds, so each carbon atom has one electron, that’s delocalised and can move.
This means that graphite, conducts, electricity, and thermal energy.
Graphene is one layer of graphite:
Explain…
Graphene is a sheet of carbon atoms joined together in hexagons. The sheet is just one atom thick, making it a two-dimensional substance. The net worth of covalent bonds makes it very strong. It’s also incredibly light so can be added to composite materials to improve their strengths without adding much weight. Like graphite it contains delocalised electrons so can conduct electricity through the whole structure. This means that has the potential to be used in electronics.
What are fullerenes and nanotubes?
Fullerenes are molecules of carbon shaped tubes that are mainly made up of carbon atoms arranged in pentagons or hexagons. Fullerenes can be used to cage other molecules such as deliver drugs into the body. They have a huge surface area so could help make great industrial catalysts or lubricants. Fullerenes can also form nanotubes, which are tiny carbon cylinders.
Nanotubes conduct, both electricity and thermal energy, they also have a high tensile strength and can be used in nano technology such as in electronics.
What is metallic bonding?
Metallic bonding involves delocalised electrons. Metals also consist of a giant structure, the electrons in the outer shell of the metal atoms are delocalised, there are strong forces of electrostatic attraction between positive metal ions and the shared negative electrons.
Substances that are held together by metallic bonding include metallic elements and alloys, it’s the delocalised electrons in a metallic bonds, which produce all the properties of metals.
Why are most metals a solid at room temperature?
The electrostatic forces between the metal atoms in at the localised electrons are very strong so need lots of energy to be broken.
This means the most compounds with a metallic bonds are very high, melting and boiling points, so they are generally solid at room temperature.
Are metals good conductors of electricity and heat?
The delocalised electrons carry electrical current and thermal heat energy through the whole structure. So metals are good conductors of electricity and heat.
Why are most metals malleable?
The layers of atoms in a metal can slide over each other, making metals, malleable, meaning they can be bent, hammered, or rolled.
Why are alloys harder than pure metals?
Pure metals are too soft when they pure, so I mixed with other metals to make them harder. Most of the metals we use every day are alloys, a mixture of two or more metals or a metal and another element. Different elements have different sized atoms, so when mixed, some metal atoms will distort, making them harder than pure metals.
What are the three states of matter?
Solid
liquid
gas
How strong forces are depends on what three things?
The type of material, the temperature, the pressure. You can use a model called particle theory to explain how the particles in a material behave in each three states of matter.
How do the particles in a solid behave?
1) They’re strong forces of attraction between particles, holding them close together in fix positions to form a very regular lattice arrangement.
2) The particles don’t move from their positions keep a definite shape and volume and don’t feel like liquids.
3) the particles vibrate about their positions, the hotter, the solid becomes, the more they vibrate.
