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Elements forming compounds. Ionic and molecular compounds. Ion: is an atom or a group of atoms that has an electric charge. When a neutral atom transfers one or more electrons to another atom , it results in the formation of an ionic compound.
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Elements forming compounds. Ionic and molecular compounds
Ion: is an atom or a group of atoms that has an electric charge. • When a neutral atom transfers one or more electrons to another atom , it results in the formation of an ionic compound. • Example: You and your friend go to a market that sells apples for 40 cents each and oranges for 50 cents each. You have 45 cents in your pocket and want to buy an apple. Your friend also has 45 cents in his pocket but wants to buy an orange. If you give your friend 5 cents he can buy an orange and you can still buy an apple. Transferring the nickel to your friend gets both of you what you want. In a simple way your actions model what can happen between atoms.
An atom that loses a valence electron becomes a positive ion. • When an atom gains an electron it gains a negative charge and becomes a negative ion. • Example: If an atom loses two electrons what charge will the ion have? Positive two (+2). If an atom gains three electrons what charge will the ion have? Negative three (- 3). • Positive ions are also called cations. • Negative ions are also called anions( when dealing with electricity). • An ionic compound is made up of positive and negative compounds. • How does an ionic compound form? The transfer of electrons from one element to another.
Page 365 figure 1 • Two elements ,potassium(K) and Fluorine (F) • Answer the following questions: • Which atom is about to lose an electron? • Which atom is in the cartoon? • What happens to the atom when it loses the electron • What happens to the fluorine atom?
Some ions are made of several atoms. • Ions that are made of more than 1 atom are called polyatomic ions. • Atoms that easily lose electrons react with atoms that easily gain electrons, thus valence electrons are transferred from one type of atom to another.(example: sodium and chlorine atoms reacting to form sodium chloride, known as table salt).
Positive and negative charges attract each other. • How does this affect positive and negative ions? They will be attracted to each other. • When an atom loses an electron, where does the electron go? To an atom that tends to gain electrons. • Oppositely charged particles attract and form an ionic bond. • When oppositely charged ions bond the result is an ionic compound. • An ionic compound is made up of positive and negative ions but the overall charge on the compound is zero. Example: The positive Na ion and the negative CL form the ionic compound NaCL which has no charge.
Naming ionic compounds • Formulas for Ionic compounds: • A chemical formula is a group of symbols that shows the ratios of elements in a compound. • Subscripts tell the ratio of elements in a compound. Example: CaCL2-the ratio of calcium ions to chloride ions is 1 to 2. • Rules for writing a formula for an ionic compound: The name of positive ion comes first, followed by the name of the negative ion. • If the negative ion is a single element the end of the name changes to –ide. Example CaO is called calcium oxide. • If the negative ion is polyatomic its name usually ends in – ate or – ite .Example NH1NO3 called ammonium nitrate.
How do molecular compounds form? • The chemical bond formed when two atoms share electrons is called a covalent bond. • Covalent bonds usually form between nonmetal atoms • What are two covalently bonded atoms called? A molecule • A molecular compound is a compound that is made up of molecules. • Example: you and your friend want to buy a sandwich that sells for 1 dollar. Each one of you has only 50 cents. If you combine your money you can buy the sandwich and share it. Similarly 2 atoms can form a bond by sharing electrons-thus covalent bond
Atoms in some covalent compounds tend to have slight electrical charges. • Atoms of some elements pull more strongly than atoms of other elements .As a result electrons are shared unequally.Unequal electron sharing causes electric charges. • Example :tug of war.Two groups pulling a rope.Rope moves towards the stronger team.Same concept with electric charges in covalent bonds. • If 2 atoms pull equally on the electrons neither atom becomes charged.This is called a nonpolar bond-a covalent bond in which electrons are shared equally. • A covalent bond in which electrons are shared unequally is a polar bond. • The atom with the stronger pull gains a negative charge. • The atom with the weaker pull gains a positive charge.
Polar bonds form when the atoms of a molecule unequally share the electrons. • Not all polar bonds result in polar molecules(positively and negatively charged). • Example : CL2 is a not a polar molecule. Molecular chlorine has a non polar bond. Molecules that are made up of two identical atoms show equal sharing of electrons, thus a nonpolar molecule..
What determines properties of metals • Each property of metals is determined by the structure of metal atoms and the bonding between their valence electrons. • Properties: shiny, bendable, can conduct heat and electricity • How does a metal’s high thermal conductivity relate to its valence electrons? The loosely attracted electrons move and transfer heat from electron to electron. • Why do metals have high luster? The valence electrons absorb light and then re emit it which gives a shiny look.
