Lecture Notes on Ions

Elements and Ions

Elements and Atoms

• An element is defined by the number of protons in its atom, which is also known as its atomic number. For example, carbon is defined by having 6 protons.

• A neutral atom of an element has an equal number of protons and electrons, maintaining electrical neutrality.- For example, a neutral carbon atom has six protons and six electrons, resulting in no net charge.

Ions

• An ion is formed when an atom gains or loses electrons, resulting in an imbalance between protons and electrons, and thus a net charge.

• If the number of protons and electrons are not equal, the atom is called an ion. Ions can be positively charged (cations) or negatively charged (anions).

• Example:- If a carbon atom has six protons and five electrons, it becomes a carbon ion with a +1 charge (C+ or C^{1+}). This is because it has one more proton than electrons.

Determining Ions and Elements

• The number of protons defines the element; altering the number of protons changes the element itself.

• Example:- An atom with five protons is boron (B). The number of protons is the defining characteristic.

  • If this boron atom has six electrons (one more than the number of protons), it becomes a boron ion with a -1 charge (B- or B^{1-}). This is because it has one more electron than protons.

Platinum Ion Example

• An atom of platinum (Pt) has a mass number of 195 and contains 74 electrons.

• Platinum, by definition, has 78 protons. The number of protons is what identifies it as platinum.

• Since this platinum atom has 74 electrons, it has four more protons than electrons, resulting in a +4 charge.- This can be written as Pt^{+4}. The charge indicates the ion's state.

Terminology

• Atom: Neutral charge when the number of protons and electrons are the same. Atoms in their neutral state have no net charge.

• Ion: Any atom or molecule with an unequal amount of protons and electrons (non-neutral). Ions have either a positive or negative charge.

• Cation: A positive ion, formed when an atom loses electrons.

• Anion: A negative ion, formed when an atom gains electrons.