Ions & Ionic Compound

Compounds A compound is a pure substance made up of two or more elements in which the elements are chemically combined + = Na Cl NaCl

Compounds Two types of compounds: Ionic and Molecular Ionic compounds: composed of positive and negative ions

Ion An ion is an atom or group of atoms that has either a positive charge or a negative charge

Ion Ions form when atoms gain or lose electrons to become stable A atom is stable when the valence shell is full

Positive Ion Example Sodium loses one electron to become stable Results in an ion that has a positive charge = Na x

Positive Ion Example The symbol “+” is written as a superscript to indicate that the sodium has a charge of 1+ Na+

Negative Ion Example Chlorine gains one electron to become stable Results in an ion with a negative charge = Cl

Negative Ion Example The symbol “-” is written as a superscript to indicate that the chlorine ion has a charge of 1- Cl-

Ion Both ions have a full valence shell containing the maximum number of electrons possible This new arrangement of valence electrons has less energy than the previous arrangement and is stable

Cation When an atom gives up one or more electrons it becomes positive Called a cation “cat-eye-on”

Anion When an atom gains one or more electron it become negative Called an anion (“an-eye-on”)

Ion Anions are negative Ca+ions are posi+ive

Writing Ion Symbols Write the symbol of the element and show the ion charge as a superscript Example: the symbol of a calcium ion is Ca2+ When an ion has a charge of 1+ or 1- the symbol has no number in the superscript, such as Na+ or F-

Naming Univalent Cations When an element can form only one type of ion, the ion has the same name as the element Eg: Ca2+ = calcium ion Ca 20p 20n +2

Naming Multivalent Cations A multivalent element is an element that can form an ion in more than one way Example: An atom of copper can form two different ions: Cu+ or Cu2+

Naming Multivalent Cations The name of an ion of a multivalent element always contains a Roman numeral that indicates the ion charge I = 1 II = 2 III = 3 IV = 4 V = 5 VI = 6

Naming Multivalent Cations For example, Cu+ is named copper(I) (read as “copper one”) Cu2+ is named copper(II) (read as “copper two”) Only multivalent metals have Roman numerals in their names

Naming Anions A nonmetal that has gained electrons to become an ion has the the same name as the element but with the ending changed to -ide Eg: Cl- = chloride ion

Naming Anions nitrogen  nitride oxygen oxide fluorine fluoride phosphorous phosphide sulfur sulfide chlorine chloride bromine bromide iodine iodide

Ion Reactivity Metal atoms tend to lose electrons Non-metal atoms tend to gain electrons

Ion Reactivity The farther the valence electron is from its positive nucleus, the more easily it is removed and the more reactive the atom is

Cation Reactivity Reactivity generally increases for cations as you move down the periodic table Example: potassium is more reactive than sodium Rubidium Potassium Cesium Lithium Sodium

Cation Reactivity Li K Na reactivity increases

Cation Reactivity Li Reactivity generally increases for cations as you move down the periodic table. But why? Na Electrons that are further away from the nucleus are more easily lost. Thus atoms with more orbitals will be more reactive. K

Anion Reactivity Reactivity generally decreases for anions as you move down the periodic table Example: fluorine is more reactive than chlorine Iodine Bromine Astatine Fluorine Chlorine

Anion Reactivity Cl F reactivity increases

Anion Reactivity Reactivity generally decreases for anions as you move down the periodic table But why? F Elements whose valence shell is closer to the nucleus will gain electrons more readily because they are closer to the nucleus. Negative electrons have a stronger attraction for the positive nucleus when the valence shell is closer to the nucleus. Cl

A metal atom that has lost electrons (cation) and a nonmetal atom that has gained electrons (anion) will have the same number of electrons as its nearest noble gas.

Cations An metal atom that has lost electrons (cation) will have the same number of electrons as its nearest noble gas.

Cations For example, neon is the closest noble gas in the periodic table to sodium, magnesium and aluminum

Cations The cations Na+, Mg2+, and Al3+ all have the same number of electrons as atoms of neon. This relationship is known as being isoelectronic (having the same number of electrons). Na 11p 12n +1 Al 13p 14n +3 Mg 12p +2 Ne 10p 10n

Anions Apply concept to anions For example, neon is the closest noble gas in the periodic table to nitrogen, oxygen and fluorine

Isoelectronic Prove that these atoms are isoelectronic by drawing the Bohr diagrams. Ne N3- O2- F-

Ionic Compounds In general, an ionic compound consists of a metal and nonmetal It is more accurate to say that ionic compounds form when atoms of different elements transfer electrons resulting in ions of opposite charges. Thus there is always an electron donor and acceptor.

Ionic Compound For example, this process occurs when atoms of sodium metal (Na) combine with atoms of chlorine (Cl) to form sodium chloride (NaCl), or table salt + = Na Cl NaCl

Ionic Compound During the formation of NaCl, one electron is transferred from a sodium atom to a chlorine atom

Ionic Compound In general, a cation will react with an anion to acquire a full valence shell

Ionic Compound The attraction between the cation and the anion is known as an ionic bond. This bond is what holds the ionic compound together.

Properties of Ionic Compound At room temperature, most are hard, brittle solids that can be crushed

Properties of Ionic Compound Ionic compounds form crystals that have an alternating arrangement of positively charged ions and negatively charged ions, so that when they break their edges are well-defined

Properties of Ionic Compound In an ionic crystal, every ion is attracted to every other ion in the crystal. As a result, ionic crystals have very high melting points ex.) NaCl melts at 800oC

Properties of Ionic Compound When an ionic compound dissolves in water, the crystal structure breaks down and the ions become free to move.

Properties of Ionic Compound Solutions of ionic compounds can conduct electricity

Naming Univalent Ionic Compounds Univalent Ionic Compounds are compounds where the metal ion only has one possible charge.

Naming Univalent Ionic Compounds Name the metal ion first The name of the metal ion is the same as the element name Example: in KBr, the name of the K+ ion is potassium Name the non-metal ion second When a non-metal becomes a negative ion, the ending of its name changes to “ide” Example: a bromine atom become bromide ion (Br -) The formulas of ionic compounds often contain numbers called subscripts which can be ignored when determining the name. Example: Na3P is sodium phosphide

Naming Univalent Ionic Compounds Example Problem 1: Write the name of the ionic compound ZnF2 Name the metal ion: Zn forms only one type of ion (Zn2+), so the name is zinc Name the non-metal ion: The atom is fluorine so the ion is fluoride Combine the names: ZnF2 = zinc fluoride

Naming Multivalent Ionic Compounds Multivalent Ionic Compounds are compounds where the metal ion only has two or more possible charges.

Naming Multivalent Ionic Compounds Identify all the possible charges of the ions. Example: FeO Fe can be Fe2+ or Fe3+ O is O2- Determine which charge on the multivalent ion is needed to make the compound neutral Example: Need to use Fe2+ to balance O2-

RULE: Although ionic compounds are made of charged particles, the compound itself has no net charge All ion charges of an ionic compound must add up to zero The positive and negative charges in an ionic compound must be equal

Naming Multivalent Ionic Compounds Identify all the possible charges of the ions. Example: FeO Fe can be Fe2+ or Fe3+ O is O2- Determine which charge on the multivalent ion is needed to make the compound neutral Example: Need to use Fe2+ to balance O2- Name the metal ion indicating the charge in brackets using Roman numerals 1 = I, 2 = II, 3 = III, 4 = IV, 5 = V Name the non-metal ion changing the ending to ‘ide’ Example: FeO = Iron (II) oxide

Naming Multivalent Ionic Compounds Example Problem 2: Write the name of the ionic compound MnCl4 Identify the ions that form the compound: Mn2+ or Mn4+ and Cl- Determine the charge of the multivalent ion that would make the compound neutral. Cl4 means there are 4 x Cl- = a total charge of 4- Would need to use Mn4+ Name the metal ion indicating the charge using Roman numerals in brackets and adding the nonmetal –ide. Manganese (IV) iodide

Polyatomic Ions Poly = 2 or more Atomic = atoms A polyatomic ion is a group of atoms, usually of different elements, that act as a single ion Example: one atom of sulphur and four atoms of oxygen form the polyatomic ion called sulphate, or SO42-

Polyatomic Ions Similar polyatomic ions are named using the suffixes “-ate” or “-ite” Example: NO3- is nitrate; NO2- is nitrite Most common polyatomic ions have a negative charge However, the ammonium ion NH4+ has a positive charge

Polyatomic Ions Name Formula ammonium NH4+ carbonate CO32- bicarbonate HCO3- hydroxide OH- nitrate NO3- nitrite NO2- permanganate MnO4- phosphate PO43- phosphite PO33- sulphate SO42- sulphite SO32-

Naming Polyatomic Ionic Compounds Example Problem 3: Write the name of the ionic compound LiHCO3 Name the metal/positive ion: Example: Li+ = lithium Identify the polyatomic ion (use table): Example: HCO3- = hydrogen carbonate Combine the names. Do not change the polyatomic ending. LiHCO3 = lithium hydrogen carbonate

Writing Chemical Formula for Uni & Multivalent Ionic Compounds Identify the charge of the ions in the compound Example: Calcium chloride Ca2+ and Cl- Determine the number of positive and negative ions needed to make the compound neutral Need 2 Cl- to balance 1 Ca2+ Write the metal atom first. Use subscript to indicate the number of ions if it is more than 1. Make sure to use on the lowest common multiple. Calcium chloride = CaCl2 Wrong: Ca2Cl4

Writing Chemical Formula for Uni & Multivalent Ionic Compounds Example Problem 4: Write the chemical formula for Bismuth (V) Phosphide. Bi5+ and P3- How many of each do we need to make the compound neutral? Write the chemical formula using subscripts as needed.

Writing Chemical Formula for Polyatomic Ionic Compounds Identify the charge of the ions in the compound Example: Calcium chlorate Ca2+ and ClO4- Determine the number of positive and negative ions needed to make the compound neutral Need 2 ClO4- to balance 1 Ca2+ Write the metal atom first. If subscripts are needed for the polyatomic ion, place a bracket around it first. Make sure to use on the lowest common multiple. Calcium chlorate = Ca(ClO4)2

Writing Chemical Formula for Polyatomic Ionic Compounds Example Problem 5: Write the chemical formula for arsenic (III) acetate. As3+ and C2H3O2- How many of each do we need to make the compound neutral? Write the chemical formula using subscripts and brackets as needed.