C6: Chemical bonding, structure and properties Flashcards
What is the difference entre pure substances, elements, compounds and mixtures?
Pure substances contain a single element or compound.
An element is a substance made from only one type of atom. Elements cannot be decomposed into simpler substances by chemical means.
A compound is a substance made from different elements bonded together.
Mixtures (for example, air or tap water) contain more than one element or compound.
halve
The elements of Group 18 are called the noble gases. Each of these elements has a full outermost shell of electrons and include helium (2), neon (2,8) and argon (2,8,8).
When atoms react to form compounds, they transfer or share electrons and obtain their full outermost shell of electrons like one of the noble gases:
Metal atoms often lose electrons
Non-metal atoms often gain extra electrons
what happens when a metal reacts w a non metal?
When a metal reacts with a non-metal, there is usually a transfer of electrons. The metal atoms lose electrons and the non-metal atoms gain electrons. The ions formed have the full electron configuration of a noble gas.
When metals react with non-metals in this way, an ionic compound is formed which is made of a giant lattice of positive and negative ions. There is an strong overall electrostatic attraction between the positive and negative ions. This is known as ionic bonding.
what happens when 2 non metals react?
When non-metals react with each other, they share electrons. When atoms share electrons, they form molecules.
The two shared electrons that join the atoms together in the molecule are called a covalent bond. Covalent bonds are generally strong.
Formation of ionic compounds ?
When a metal reacts with a non-metal, there is usually the transfer of electrons. The metal atoms lose electrons and the non-metal atoms gain electrons. An ionic compound is formed which is made of a giant lattice of positive and negative ions.
Ion charges?
When atoms react to form ions, they gain/lose electrons and obtain the electron configuration of a noble gas. Therefore the charge of these ions depends on the electron configuration of the atoms. For example, atoms in Group 1 of the Periodic Table have one electron in their outer shell and so lose one electron forming 1+ ions. Group 1 1+ Group 2 2+ Group 13 3+ Group 16 2– Group 17 1–
Combinations of atoms can also exist as overall charged ‘compound ions’.
There are some other common ions whose formulae and charges should learned:
Combinations of atoms can also exist as overall charged ‘compound ions’.
There are some other common ions whose formulae and charges should learned:
hydrogen H+ ammonium NH4+ hydroxide OH− nitrate NO3− sulfate SO42− carbonate CO32− phosphate PO43−
Properties of ionic compounds?
Ionic compounds are generally solids at room temperature. They are made of a giant lattice of positive and negative ions. A lattice is a huge, continuous, regular structure.
There is a strong overall electrostatic attraction between all of the positive and negative ions. This means that ionic compounds have high melting points as it is difficult to overcome the many strong attractions between the positive and negative ions.
Ionic compounds generally do not conduct electricity as solids because the ions cannot move around freely. However, if a compound is melted, it does conduct electricity because the ions can move and carry the charge. Many ionic compounds dissolve in water and will conduct as a solution because the solvated ions can move to carry the charge.
Formation of covalent bonds?
When non-metals react with each other, they each will gain extra electrons. They can do this by sharing electrons. The two shared electrons that join the atoms together are called a covalent bond.
Describe molecular cv substance examples
Most substances that contain covalent bonds are made up of many molecules. Each molecule contains a specific number of atoms joined by covalent bonds.
Methane (CH4) is an example of a substance made of small molecules, with each molecule containing one carbon and four hydrogen atoms.
Glucose (C6H12O6) is another example of a substance made of molecules, but larger ones containing six carbon, twelve hydrogen and six oxygen atoms.
What kind of pmts and bpts? do molecular cvs have?
Within each molecule, the atoms are joined by covalent bonds. However, the molecules are not joined to each other. There are only weak attractive forces between molecules. This means that it is easy to overcome the weak forces between the molecules and so molecular substances usually have low melting and boiling points
Describe giant cvs
Giant covalent substances
Some covalent substances are made up of a single, giant lattice. Common examples are diamond (C), graphite (C) and silicon dioxide (SiO2). The lattice is a continuous network of atoms linked by covalent bonds.
Giant covalent substances have very high melting and boiling points because all of the strong covalent bonds have to be broken when they melt and boil.
Graphite conducts electricity because it contains some delocalised electrons that can move along the layers. However, most giant covalent substances do not conduct electricity because they do not contain any delocalised electrons.
Diamond and silicon dioxide are very hard due to the rigid network of atoms linked by covalent bonds. However, graphite is soft because the layers of covalently bonded atoms are not bonded to each other and so can slide over each other.
describe metals
In metals (as solids and liquids), the outer shell electrons are delocalised (free) and can move throughout the metal. This means that solid metals effectively consist of a lattice of positively charged ions surrounded by delocalised electrons.
Properties of metals?
Most metals have high melting points because the metallic bonding is strong. This is because there is a strong overall attraction between the positive metal ions and the negative delocalised electron cloud.
Metals conduct electricity because the outer shell electrons are delocalised and can carry charge through the metal.
Metals are malleable (can be hammered into shape) because the metal ions can move relative to each other while maintaining the metallic bonding.
summarise ionic
Ionic
Giant lattice of positive and negative ions. There is a strong electrostatic attraction between the positive and negative ions.
Melting and boiling points: HIGH due to the strong attraction between the positive and negative ions.
Conductivity:Not a conductor as solid (ions cannot move).
Conductor when molten or dissolved (as ions can move to carry charge).
