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.
Explain how sodium chloride would form an ionic bond
An atom of sodium will lose an electron and form a positive ion.
An atom of chlorine will gain an electron and form a negative ion.
What is an ionic bond?
The ionic bond is the electrostatic force of attraction between a positively charged metal ion and a negatively charged non-metal ion. (Transferring electrons)
Explain why metals form positive ions
Metals form positive ions because they lose electrons to become stable.
Magnesium (Mg) has the electron arrangement 2,8,2.
To become stable it must lose its two outer electrons to obtain a full outer energy level.
Explain why atoms are neutral
Atoms are neutral because they have equal numbers of protons and electrons however, when they lose two electrons they are no longer neutral. They change into ions with a two positive charge.
Explain why non-metals form negative ions
Non-metals form negative ions because they gain electrons to become stable.
Chlorine (Cl) has an electron arrangement 2,8,7.
To become stable it must gain an electron to obtain a full outer energy level.
What is an ionic lattice?
Ionic compounds form what is known as a lattice structure. This is a regular repeating arrangement of metal and non-metal ions. (A cube of tightly packed alternate metal and non-metal ions.)
Descibe the properties of an ionic lattice
Ionic lattices have very high melting points and conduct when molten or in solution but never when solid
Ionic compounds dissolve in water easily, what happens when they do this?
Ionic compounds dissolve in water easily, when they do this their lattice breaks up completely and water molecules surround the seperated ions. Therefore they can conduct as their ions are free to move.
What is metallic bonding?
Metallic bonding is the strong electrostatic force of attraction between the metal ions and the delocalised electrons.
Describe the properties of a metallic bond
Metallic bonds have a high melting point and a high boiling point, metallic bonds are very strong
Summarise the properties of covalent bonds
Covalent Bonds:
Conductivity
Solid - insulator
Liquid - insulator
Aqueous solution - insulator
Solubility
Water - insoluble
Other covalent liquids - insoluble
Melting point - low
Boiling point - low
Summarise the properties of covalent network
Covalent Networks:
Conductivity
Solid - insulator except graphite
Liquid - insulator except graphite
Aqueous solution - insulator
Solubility
Water - insoluble
Other covalent liquids - insoluble
Melting point - very high
Boiling point - very high
Summarise the properties of ionic bonds
Ionic Bonds:
Conductivity
Solid - insulator
Liquid - conductor
Aqueous solution - conductor
Solubility
Water - insoluble
Other covalent liquids - insoluble
Melting point - high
Boiling point - high
Summarise the properties of ionic lattices
Ionic lattices:
Conductivity
Solid - insulator
Liquid - conductor
Aqueous solution - conductor
Solubility
Water - insoluble
Other covalent liquids - insoluble
Melting point - high
Boiling point - high
Summarise the properties of metallic bonds
Metallic bonds:
Conductivity
Solid - conductor
Liquid - conductor
Aqueous solution - do not form solutions
Solubility
Water - insoluble
Other covalent liquids - insoluble
Melting point - high
Boiling point - high
Explain why ionic compounds have high melting and boiling points
All ionic compounds have a high melting point and boiling point because many strong ionic bonds need to be broken.
Explain why ionic compounds conduct when molten and in solution
They conduct when molten or in solution as the ions are free to move. They are generally soluble in water.
What can ionic compounds be broken down by?
They can be broken down by electrolysis
Explain why covalent network structures have very high melting and boiling points
All covalent network structures have very high melting points and boiling points because many strong covalent bonds need to be broken.
Why do covalent network structures not conduct electricity, and do they dissolve?
They are all hard, and do not conduct electricity because there are no free charges that can move. They do not dissolve.
Explain why covalent bonds have low melting and boiling points
They have low melting points and boiling points because the attractions between molecules are easy to overcome.
Why do covalent bonds not conduct electricity, and do they dissolve?
They do not conduct electricity because there are no free charges to move. Most do not dissolve in water but may dissolve in other solvents.
