ions

atoms to ions

Atoms cannot only gain extra electrons. They can also lose electrons. In either case, they become ions. Ions are atoms that have a positive or negative charge because they have unequal numbers of protons and electrons. If atoms lose electrons, they become positive ions, or cations. If atoms gain electrons, they become negative ions, or anions. Consider the example of fluorine (see Figure 1.1). A fluorine atom has nine protons and nine electrons, so it is electrically neutral. If a fluorine atom gains an electron, it becomes a fluoride ion with an electric charge of -1.

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names and symbols

Like fluoride, other negative ions usually have names ending in -ide. Positive ions, on the other hand, are just given the element name followed by the word ion. For example, when a sodium atom loses an electron, it becomes a positive sodium ion. The charge of an ion is indicated by a plus (+) or minus sign (-), which is written to the right of and just above the ions chemical symbol. For example, the fluoride ion is represented by the symbol F , and the sodium ion is represented by the symbol Na+ . If the charge is greater than one, a number is used to indicate it. For example, iron (Fe) may lose two electrons to form an ion with a charge of plus two. This ion would be represented by the symbol Fe2+ . This and some other common ions are listed with their symbols in the Table 1.1. Cations Name of Ion Calcium ion Hydrogen ion Iron(II) ion Iron(III) ion Chemical Symbol Ca2+ H+ Fe2+ Fe3+ Anions Name of Ion Chloride Fluoride Bromide Oxide Chemical Symbol Cl F Br O2 Q: How does the iron(III) ion differ from the iron(II) ion? A: The iron(III) ion has a charge of +3, so it has one less electron than the iron(II) ion, which has a charge of +2. Q: What is the charge of an oxide ion? How does its number of electrons compare to its number of protons? A: An oxide ion has a charge of -2. It has two more electrons than protons.

how ions form

The process in which an atom becomes an ion is called ionization. It may occur when atoms are exposed to high levels of radiation. The radiation may give their outer electrons enough energy to escape from the attraction of the positive nucleus. However, most ions form when atoms transfer electrons to or from other atoms or molecules. For example, sodium atoms may transfer electrons to chlorine atoms. This forms positive sodium ions (Na+ ) and negative chloride ions (Cl ). Click image to the left or use the URL below. URL:

properties of ions

Ions are highly reactive, especially as gases. They usually react with ions of opposite charge to form neutral compounds. For example, positive sodium ions and negative chloride ions react to form the neutral compound sodium chloride, commonly known as table salt. This occurs because oppositely charged ions attract each other. Ions with the same charge, on the other hand, repel each other. Ions are also deflected by a magnetic field, as you saw in the opening image of the northern lights.

atoms are neutral

The northern lights arent caused by atoms, because atoms are not charged particles. An atom always has the same number of electrons as protons. Electrons have an electric charge of -1 and protons have an electric charge of +1. Therefore, the charges of an atoms electrons and protons cancel out. This explains why atoms are neutral in electric charge. Q: What would happen to an atoms charge if it were to gain extra electrons? A: If an atom were to gain extra electrons, it would have more electrons than protons. This would give it a negative charge, so it would no longer be neutral.

instructional diagrams

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questions

an iodine atom has 53 protons. how many electrons does an iodine anion have?

-->  a) at least 54

b) 53 or more

c) 53 or less

d) none of the above

what is the name of the ion represented by the following symbol? o2-

a) oxygen ion

b) dioxide

-->  c) oxide

d) none of the above

the process in which ions form is called ionization.

-->  a. true

b. false

ways in which ions may form include

a) exposure to radiation.

b) transfer of electrons between atoms.

c) sharing of electrons between atoms.

-->  d) two of the above

ions are very unreactive.

a. true

-->  b. false

ions are deflected by a magnetic field.

-->  a. true

b. false

diagram questions

No diagram questions associated with this lesson