Atomic Structure and Bonding Flashcards
What does the nucleus contain?
Protons and neutrons
What does the shell contain
Electrons
How can compounds form?
Energy transfer
How can you break an ionic compound?
Provide enough energy
Why is there a stronger force of attraction between MgO than NaCl?
It is mg2+O2- so there is a stronger force of attraction between the oppositely charged ions. Because there are larger opposite charges
What is electrical current?
The movement of charged particles such as ions or electrons in a circuit.
How many bonds can an atom form?
As many bonds as there are electrons in its outermost shell.
What is a covalent bond?
A shared pair(s) of electrons between 2 atoms. There is an attractive force between the pair of electrons and the protons in the nuclei of the atoms involved in forming the bonds.
What is an atom?
The defining structure of an element made up of protons, neutrons and electrons. The smallest part of a chemical element that can exist.
What is an intermolecular force?
The forces of attraction between separate molecules. They can be repulsive.
What is a molecule?
A fixed number of covalently bonded atoms. (Two or more covalently bonded atoms)
What is metallic bonding?
The electrostatic force of attraction between positive metal ions and the sea of delocalised electrons
Why are metals good conductors of electricity?
Because they have a sea of delocalised electrons that are free to move where current can pass through
Why do metals have a high melting point?
Because more energy is needed to break the strong electrostatic forces of attractions (bonds) between the metal ions and sea of delocalised electrons.
Give 3 examples of a giant covalent structure
Carbon (diamond) Carbon (graphite) SiO2
In a simple molecule what do you have to break to melt the substance?
Intermolecular forces of attraction
Why are metals malleable?
The layers of ions can slide over each other easily.
How many other carbon atoms is each carbon atom bonded to in diamond?
4
How many carbon atoms is each carbon atom bonded to in graphite and what does this mean?
3, that there is a delocalised electron
What are the forces of attraction between layers of graphite like?
Weak
Why is graphite a good conductor of electricity?
Because of the delocalised electrons that haven’t been used and the current can pass through
What is graphene?
One layer of graphite
Why do giant covalent structures have such a high melting point
Because to melt it you need to break every covalent bond in the giant structure
What is the force of attraction between the metallic ions and delocalised electrons?
Electrostatic force of attraction
Give an example of a giant ionic structure
Sodium chloride Anything else
Describe the diagram of a metallic bond
Layers of positively charged ions surrounded by a ‘sea’ of delocalised electrons Layers of ions in a giant structure i.e. circles with plus signs in with a label around saying sea of delocalised electrons
Give an example of a simple molecular structure
H2O
Why do ionic substances have a high melting point?
Because it is a giant ionic structure so more energy is required to break the attractive forces (electrostatic forces of attraction) between the positively and negatively charged ions.
When can ionic substances conduct electricity and why?
When they are molten or in a solution (liquid) because the positive and negative ions are free to move so can carry an electric current.
Why do simple molecular substances have low melting points?
Because only enough energy is needed to break the weak intermolecular forces between molecules
Do all covalent bonds conduct electricity?
NO (except graphite and graphene)
When can ionic substances not conduct electricity and why?
When they are solid because the ions are locked together in a lattice/giant structure so the ions (which would be the charge carriers) are not free to move in a fixed regular structure
Why don’t covalent bonds conduct electricity?
Because there are no charged particles free to move
Describe an ionic crystal shape
Giant three-dimensional regular lattice structure
What are properties that ionic compounds have?
High melting point High boiling point Dissolve easily in water (They are soluble)
What is a diatomic molecule?
One that contains two atoms.
What does an ethane dot and cross diagram look like?
two carbons with a shared pair of electrons, and then each with three hydrogens covalently bonded to it.
What does a carbon dioxide dot and cross diagram look like?
two oxygens covalently bonded to carbon, both with double covalent bonds.
What does an ethene dot and cross diagram look like?
two carbons with a double covalent bond and then each carbon respectively bonding with two hydrogens, single bond.
What does an nitrogen dot and cross diagram look like?
two nitrogens with a triple covalent bond.
what is an ion?
An atom or group of atoms which carries an elecrical charge, either positive or negative.
what are the names of positive and negative ions?
a positive ion is a cation a negative ion is an anion
When writing the symbol for a metal in exams such as sodium, should you write Na or Na+?
Thinking about the structure as a whole you write Na as the number or electrons balances the number of positive charges. The metal as a whole has no charge.
What happens to the bonds when you melt or boil a substance made of molecules?
You are breaking the intermolecular forces NOT the covalent bonds. When you boil water you get steam, not a mixture of hydrogen and oxygen atoms. The covalent bonds within the molecule remain (it is still H2O)
What is ionic bonding?
Bonding in which there has been a transfer of electrons from one atom to another to produce ions. The substance is held together by strong electrical attractions between positive and negative ions.
Simple physical properties of a metal:
Metals tend to be strong high melting and boiling point.
HOW are metals good conductors of heat?
If you heat one end of the metal the energy is picked up by the delocalised electrons and as the electrons move around in the metal the heat energy is transferred throughout the structure.
What would happen if you subjected a metal to a small force?
It will stretch and return to its original position, it is elastic.
What would happen if you subjected a metal to a large force
The particles slide over each other and stay in their new positions.
What is an alloy? Give some examples:
An alloy is a mixture of metals. Brass is an alloy of copper and zinc, stainless steel is an alloy of iron, chromium and nickel.
What is a lattice?
A regular array of particles.
What does ductile mean?
Can easily side over each other and be drawn into wires
How would you draw an ionic structure, e.g. NaCl
Draw two particles in the key, e.g. Na+ as a black dot and Cl- as a blank dot. Draw lots of cubes with a particle on each corner, make sure there are never any two Na+ connected by lines and visa versa.
Why are ionic substances usually soluble in water? (May be extra)
The electrons in the bonds are attracted towards the oxygen end of the bond. This makes the oxygen slightly negative leaving the hydrogen slightly short of electrons and therefore slightly positive. Because of this distortion water is described as a polar molecule. There are quite strong attractions between the polar water molecules and the ions in the lattice. The slightly positive hydrogens in the water molecules cluster around the negative ions and the slightly negative oxygens are attracted to the positive ions.
Why isn’t magnesium oxide, an ionic substance, soluble in water?
Magnesium ions are Mg+ and oxygen ions are O2- meaning they have stronger attractions between the positively and negatively charged ions. The water molecules are not strong enough to break these bonds.
Why doesn’t diamond conduct electricity?
All the electrons in the outer levels of the carbon atoms are tightly held in covalent bonds between the atoms. None are free to move around.
Simple properties of giant covalent compounds?
Very hard Very high melting and boiling point Do not conduct electricity (except graphite) Does not dissolve in water or any solvent
Is graphite more or less dense than diamond? Why?
Graphite is less dense because the layers in graphite are relatively far apart. In a sense a graphite chrystal contains a lot of wasted space which there isnt in a diamond.
How are the layers in graphite easily removed?
Although the forces holding the atoms together in each layer are very strong, the actual forces between the layers are much weaker. The layers are relatively far apart.
Properties of simple molecular structures:
Low melting and boiling point Do not conduct electricity Tend to be insoluble to water unless they react to it Often soluble in organic solvents
What is a compound?
two or more elements in fixed proportions, joined by strong bonds.
Key differences between mixtures and compounds:
• Compounds are in fixed proportions, mixtures aren’t. • In a mixture of elements, the elements still have their own properties. But elements in a compound will not retain the same properties. • Mixtures can be separated by physical means, for compounds you must change them chemically to separate them. • There are no energy changes involved in a mixture where as when compounds are made energy is released.
Explain how an ionic compound forms (using the example of magnesium and chlorine to form MgCl2)
When magnesium atoms react with each chlorine atoms the magnesium atoms lose two electrons forming Mg2+ because it gives them to each of the two chlorine atoms, that gain one electron, each forming 2 Cl- ions
