Simple molecular substances Flashcards
Key concepts in chemistry
Atom
definition
The smallest part of an element that can exist.
Charge
definition
Property of matter that causes a force when near another charge. Charge comes in two forms, positive and negative. For example, a negative charge causes a repulsive force on a neighbouring negative charge.
Charged particles
Definition
Particles, usually ions or electrons, that carry electrical charges.
Compound
definition
A substance formed by the chemical union of two or more elements.
Covalent bond
Definition
A bond between atoms formed when atoms share electrons to achieve a full outer shell of electrons.
Double bond
Definition
A covalent bond resulting from the sharing of four electrons (two pairs) between two atoms.
intermolecular forces
Definition
Weak attractive forces between molecules. When a simple molecular substance melts or boils, it is the intermolecular forces that are broken (not the covalent bonds in each molecule).
molecular
definition
Refers to a substance made up of molecules, so it contains small groups of atoms, of a set size, held together by covalent bonds.
molecule
definition
A collection of two or more atoms held together by chemical bonds.
What is a covalent bond formed between?
A covalent bond is formed when a pair of electrons is shared between two atoms, usually non-metals.
What do molecules consist of?
A molecule consists of a group of two or more atoms joined together by covalent bonds.
Molecule
A molecule consists of a group of two or more atoms joined together by covalent bonds. Molecules of the same element or compound will have a set size - in other words, they will always contain the same number of atoms of each element. For example, a molecule of methane, CH4, will always contain one carbon atom and four hydrogen atoms.
A simple molecule can be modelled by drawing its structure.
In these structures what are atoms and covalent bonds show as?
show each atom by its element symbol
show each covalent bond as a straight line
Melting and boiling points of simple molecular substances.
Simple molecular substances generally have low melting points and boiling points and are often liquids or gases at room temperature.
What are melting and boiling points examples of?
State changes
Describe how the forces of attraction are overcome in melting or boiling?
some forces of attraction are overcome during melting, allowing molecules to move over each other
more of the forces of attraction are overcome during boiling, allowing the molecules to move freely away from each other
Comparison of strength of intermolecular forces
simple molecules and covalent bonds
reference boiling and melting points
There are intermolecular forces between simple molecules. These intermolecular forces are much weaker than the strong covalent bonds in molecules. When simple molecular substances melt or boil, it is these weak intermolecular forces that are overcome. The covalent bonds are not broken. Very little energy is needed to overcome the intermolecular forces, so simple molecular substances usually have low melting and boiling points.
A substance can conduct electricity if:
it contains charged particles, and
these particles are free to move from place to place
Can simple molecules conduct electricity?
Simple molecules have no overall charge, or charged particles that can separate, so simple molecular substances cannot conduct electricity, even when liquid or dissolved in water.
D o simple molecules have a charge?
Simple molecules have no overall charge, or charged particles that can separate
