Have you ever wondered why … Salt crystals take on their particular shape? Ionic Bonding
Ionic Bonds TRANSFER of electrons Metal and nonmetal Cation + anion Metals lose their valence e- and become positively charged Nonmetals gain enough e- to have a full outer shell (octet, or 8) and become negatively charged Opposites attract! Ionic compounds are formed – Electrostatic forces hold ions together
Valence Electrons Valence electrons are the number of electrons on the outer shell. These are the electrons involved in bonding. The number of valence electrons depends on the group!
Valence Electrons The number of valence electrons depends on the group. For example, Na is in Group 1 so it has 1 valence electron and Cl is in Group 17 so it has 7 valence electrons. Using the valence electrons, a Lewis Dot Diagram can be drawn.
Drawing Lewis Dot Diagrams A Lewis Dot Diagram is a visual interpretation of the number of valence electrons in an atom or ion. For example, Chlorine, Cl, has 7 valence electrons because it is in Group 17. Its Lewis Structure would be:
Drawing Lewis Dot Diagrams In the same respect, sodium is in Group 1 so it has one valence electron. It would have a Lewis Dot Diagram like:
Lewis Dot Diagrams Because neither Na nor Cl has achieved the Noble Gas electron configuration (Octet Rule), sodium will give up an electron to chlorine making sodium positive and chlorine negative. The 2 are then attracted to each other due to their opposite charges.
Using the PT to determine charge of ions All atoms tend to gain or lose electrons so that they will have a noble gas electron configuration (which is stable) We can look at the spaces separating an element and the nearest noble gas If the closest one is before the element, we move backwards on the PT, losing electrons (equal to # of spaces) and obtaining a positive charge If the closest noble gas is after the element, count the spaces forward, that is how many electrons must be gained, thus resulting in a negative charge
Ions Metals tend to LOSE electrons, from their outer energy level – Sodium loses one: there are now more protons (11) than electrons (10), and thus a positively charged particle is formed = “cation” – The charge is written as a number followed by a plus sign: Na 1+ – Now named a “sodium ion”
Ions Nonmetals tend to GAIN one or more electrons – Chlorine will gain one electron – Protons (17) no longer equals the electrons (18), so a charge of -1 – Cl 1- is re-named a “chloride ion” – Negative ions are called “anions”
Properties of Ionic Bonding Hard, brittle, crystalline solids at room temperature High melting and boiling points DO NOT conduct as solids DO conduct when melted or dissolved in water Most are soluble in water Called salts
Metallic Bonding Cations in a sea of electrons – Only occurs in pure metal elements and mixtures Properties include – Malleable, can be flattened into thin sheets – Ductile, can be pulled into wire – Bendable/shapeable vs brittle ionic compounds Alloys – metal mixtures, designed for specific qualities – Durability, strength, resistance to corrosion, lightweight, etc.
Metallic Bonding The “sea of electrons” or delocalized electrons are that give metallic bonds their characteristics