2-1 Atoms And Ionic Bonds

Elements Forming Compounds Chapter 2

Atoms and Ionic Bonds

Chapter 2, Section 1

Inside an Atom Structure of an Atom  Atoms consists of 3 particles: proton, & neutron (nucleus), electron

Valence Electrons

 Protons carry + charge  Electrons carry – charge  Neutrons carry neutral charge  Equal numbers of protons and electrons  Atoms have a balanced charge

 Valence electrons are electrons that are either farthest away from nucleus or most loosely held b y the nucleus  Number of valence electrons is the key to how an atom reacts with other atoms because valence electrons are involved in bonding  Electron dot diagram- consists of the symbol for an element surrounded by dots

What are the three particles found in atoms? How do they differ?

Valence Electrons and the Periodic Table  Elements in the same group of the periodic table usually have the same number of valence electrons in their atoms  Therefore, they share certain physical and chemical properties  When atoms react, either the number of valence electrons increases to eight or all are lost  The atom becomes chemically stable with 8 valence electrons

Electron Transfer and Bonding  When atoms have fewer than four valence electrons, they can transfer these to other atoms that have more than four  Ion- an atom or group of atoms that has become electrically charged  When an atom loses an electron, it loses a negative charge and becomes a positive ion  When an atom gains an electron, it gains a negative charge and becomes a negative ion

Ionic Bond- the attraction Forming an Ionic Bond Forming between two oppositely charged ions an Ionic Compounds are electrically neutral Bond NaCl

Polyatomic Ions Polyatomic Ions- ions made of more than one atoms Each polyatomic ion as a group of atoms has an overall + or – charge If a polyatomic ion combines with another ion of opposite chare, an ionic compound forms CO3 2- and Ca

2+

form CaCO3

Naming Ionic Compounds

MgO: Magnesium Oxide Na2CO3: sodium carbonate

 For an ionic compound, the name of the positive ion comes 1st, followed by the negative ion  Name of the + ion is usually a metal or a positive polyatomic ion  End of the name of – ionic element changes to –ide  If – ion is polyatomic, its name is unchaged

Physical Properties of Ionic Compounds

Physical properties of ionic compounds include crystal shape, high melting points, and electrical conductivity

Crystal- ions form an orderly, three-dimensional arrangement called a crystal Every ion is attracted to ions near that have an opposite charge NaCl crystal

Crystal Shape

High Melting Points When particles have enough energy to overcome the attractive forces between them, they break away from each other Ionic bonds are strong enough to cause all ionic compounds to be solids at room temperature

Electrical Conductivity  Electricity is the flow of electric charge, and ions have electric charges  Solid ionic compounds do not conduct electricity well  When ionic compounds dissolve in water, the solution conducts electricity  Melting ionic compounds also allows them to conduct electricity because particles move