Recall that an electron has a negative charge, while a proton has a positive charge. That means when an electron is removed from an atom, the number of electrons become fewer than the number of protons, and since protons carry a positive charge, the whole atom now carries a positive charge, and this positively charge atom is called a cation. Likewise when an electron is added to an atom, the number of electrons become more than the number of protons, and since electrons carry a negative charge, the whole atom now carries a negative charge, and this negatively charged atom is called an anion.
Now lets use the following examples to further explain how atoms for ions. In neutral sodium atom, you have 11 electrons and 11 protons.
Here is model showing the number of each:. When neutral sodium loses an electron it becomes a sodium cation. Why does oxygen form a 2 ion? An electrically-neutral oxygen atom gains two electrons to form an oxygen ion with two negative charges. Notice how the charge conserves in this process. This particular arrangement ensures two filled main energy levels while leaving the rest empty.
How do atoms form positive ions? Ions form when atoms gain or lose electrons. Since electrons are negatively charged, an atom that loses one or more electrons will become positively charged; an atom that gains one or more electrons becomes negatively charged. How do atoms form negative ions? Forming ions Metal atoms lose the electron, or electrons, in their highest energy level and become positively charged ions. Non-metal atoms gain an electron, or electrons, to become negatively charged ions.
What is meant by covalent bond? A covalent bond, also called a molecular bond, is a chemical bond that involves the sharing of electron pairs between atoms.
These electron pairs are known as shared pairs or bonding pairs, and the stable balance of attractive and repulsive forces between atoms, when they share electrons, is known as covalent bonding. How do atoms gain electrons? When atoms lose or gain electrons, they become what are called ions.
Cations have more protons than electrons and so have a net positive charge. Zwitterions are neutral and have both positive and negative charges at different locations throughout the molecule. Anions are generally larger than the parent molecule or atom, because the excess electrons repel each other and add to the physical size of the electron cloud.
Cations are generally smaller than their parent atom or molecule due to the smaller size of their electron clouds. Monoatomic ions are sometimes also represented by Roman numerals, which designate the formal oxidation state of the element, whereas the superscripted numerals denote the net charge. These representations can be thought of as equivalent for monoatomic ions, but the Roman numerals cannot be applied to polyatomic ions. Ions can be formed by ionization, which is the process of a neutral atom losing or gaining electrons.
Generally, the electrons are either added to or lost from the valence shell of an atom; the inner-shell electrons are more tightly bound to the positively charged nucleus and so do not participate in this type of chemical interaction. Ionization generally involves a transfer of electrons between atoms or molecules.
Ions form when atoms lose or gain electrons to obtain a full outer shell:. Metal atoms lose electrons from their outer shell when they form ions:. For elements in groups 1, 2 and 3, the number of electrons lost is the same as the group number. The outer shells of non-metal atoms gain electrons when they form ions:.
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