Positive Ions
- Electrons in the outer energy level can be knocked out from an atom
- This can happen in a number of ways:
- When objects are rubbed together, electrons can be removed by friction
- When electrons absorb electromagnetic radiation they can gain enough energy to leave the atom
- From chemical reactions
- When one or more electrons are removed from an atom, it becomes positively charged
- This is because an electron is negatively charged
- The atom becomes a positive ion
- An ion is an atom or particle with a non-zero charge
When radiation passes close to atoms it can knock electrons out, leaving the atom with an overall positive charge
- Ions are more chemically reactive than atoms because of their positive charge
Worked example
Which option describes the change that a Ca (Calcium) atom would undergo in order to form a Ca2+ ion?
A The atom has gained two protons
B The atom has lost two protons
C The atom has gained two electrons
D The atom has lost two electrons
ANSWER: D
- The answer is not A because a change in the number of protons would cause the element symbol to change
- The answer is not B because a change in the number of protons would cause the element symbol to change and losing protons would result in a more negatively charged particle
- The answer is not C because gaining electrons would make a particle more negatively charged
- The answer is D because an electron carries a charge of -1
- The charge on an atom is 0
- When 2 electrons are lost from an atom then it will lose two lots of -1 charge
- The new charge can be worked out as:
0 - 2(-1) = +2
Examiner Tip
Definitions are very important for picking up marks on this topic. Be clear with your definitions such as ions and isotopes, and remember that ions have different numbers of electrons, whereas isotopes have different numbers of neutrons.
