Bonding and properties of materials Flashcards
Explain what is meant by ‘a stable electron arrangement’
Atoms can be held together by chemical bonds. When atoms form bonds, they can achieve a stable electron arrangement. To achieve a stable electron arrangement atoms can lose, gain or share electrons.
What is a covalent bond and in what elements does it occur?
A covalent bond is a shared pair of electrons between atoms of two non-metal elements. (Sharing electrons)
Explain a covalent bond
A covalent bond happens when the positive nuclei from two different atoms are held together by their common attraction for the shared pair of electrons held between them.
Are covalent bonds strong or weak bonds?
Covalent bonds are strong bonds.
What happens when atoms share pair of electrons?
Atoms that share pairs of electrons form molecules. A molecule is a group of atoms held together by covalent bonds.
What is a diatomic molecule?
A diatomic molecule is a molecule containing only two atoms.
Name the diatomic molecules
There are seven diatomic elements: Iodine Bromine Chlorine Fluorine Oxygen Nitrogen Hydrogen (BrINClHOF)
State and explain the terms used to describe the shape of a molecule
Linear - between two atoms, for example, hydrogen atoms have only one electron, so if two hydrogen atoms form a single covalent bond, both can have a full outer shell and create a linear shape. H-H
Bent - between three atoms, for example, oxygen atoms have six outer electrons so need two more for a full outer shell. The oxygen forms two single covalent bonds with the two hydrogen atoms.
Trigonal pyramidal - between four atoms, for example, nitrogen atoms have five outer electrons so needs three more for a full outer shell. Nitrogen forms three single covalent bonds to hydrogen atoms.
Tetrahedral - between five atoms, for example, carbon atoms have four outer electrons so need four more for a full outer shell. The carbon forms four single bonds to the hydrogen atoms, so all the atoms now have a full outer shell of electrons.
Explain what happens when more than one bond is formed between atoms
More than one bond can be formed between atoms leading to double and triple bonds. Examples of these are diatomic oxygen (double bond) or nitrogen (triple bond).
What state are most covalent molecules in at room temperature and explain why?
Substances that consist of covalent molecules are usually gases or liquids at room temperature because the attractions between molecules are weak and easy to overcome.
What is a covalent network?
A covalent network is a substance that is a solids with a high melting point. They have much larger molecules and their structure consists of a giant 3-dimensional lattice of covalently bonded atoms.
Name some examples of covalent networks
Boron, carbon and silicon are all examples of covalent network elements.
Describe the structure of diamond
Diamond has a tetrahedral structure.
Describe the structure of graphite
Graphite has a layered, planar structure.
What are ionic bonds formed between?
Ionic bonds are formed between a metal and non-metal, for example sodium chloride.
