LEARNING GOAL
By the end of this lesson, I will be able to:
By the end of this lesson, I will be able to:
SUCCESS CRITERIA
By the end of this lesson, I will be able to:
By the end of this lesson, I will be able to:
Matter is anything that has mass and occupies space. It can be it can be divided into groups: pure substances and mixtures.
A pure substance has a constant composition: all parts of the substance are the same. This means that their properties also remain constant. In chemistry, pure substances are referred to as chemicals. For example, copper and methyl alcohol are pure substances. Pure substances can be divided further into compounds and elements. Compounds are molecules made up of more than one type of atom, such as H2O or NaCl. Elements are made up of the same kind of atom, such as Ca or Br2.
Mixtures display varying properties as the proportions of the components in the mixture change. Mixtures can be divided into two groups: heterogeneous and homogeneous. In homogeneous mixtures, all parts look the same. For example, tomato ketchup is made up of tomatoes, vinegar, salt and spices, but you can't see these parts individually in the mixture, although with a microscope you could see particles of tomato skin and pepper flakes. In chemistry, homogeneous mixtures are often referred to as solutions. On the other hand, heterogeneous mixtures are made up of parts that can be macroscopically distinguished in the mixture. For example, relish is made up of cucumbers, vinegar, red peppers, mustard seeds and spices. It is possible to see each one of these ingredients in the mixture.
The atom is the smallest particle of a chemical element that can exist on its own, and that retains its characteristic chemical properties. It is made up of three main components. The protons and neutrons form the dense nucleus in the center of the atom. The electrons travel around the nucleus.
An ion is an atom that has lost or gained electrons. A positive ion is called a cation, and a negative ion is called an anion. Thus, when a sodium atom loses an electron (which is a negatively charged particle within the atom) the sodium becomes a cation.
The atomic number of an atom corresponds to the number of protons the atom has. For a neutral atom, it is also equal to its number of electrons. The atomic number is represented by the letter Z.
The sum of the number of neutrons and protons in an atom is called the mass number. It is represented by the letter A.
The number of neutrons in a given atom can be calculated using the formula:
Neutrons = mass number – atomic number
= A - Z
Example
Iron has an atomic number 26. Its mass number is 56. The number of neutrons it contains is:
Neutrons = mass number – atomic number
= 56 – 26
= 30
Therefore, iron atoms have 30 neutrons.
Isotopes are atoms of an element that have the same number of protons but different numbers of neutrons. Isotopes are named by stating the element's name followed by its mass.
Example
The element carbon has 3 isotopes: carbon-12, carbon-13 and carbon-14. Since all carbon atoms have 6 protons, carbon-12 has 6 neutrons, carbon-13 has 7 neutrons and carbon-14 has 8 neutrons.