Atoms and Bonding Chapter 5

Atomic Structure and the Periodic Table Review the structure of the atom Protons? Neutrons? Electrons? Nucleus? Electron Cloud?

electron clouds nucleus

Protons (+) Neutron (0) Valence electrons Electron (-) P+ N A simplified slide Neutron (0)

Atomic Structure and the Periodic Table (cont) Electrons (negative) move around the nucleus in the electron cloud. The electron cloud has different energy shells (or orbits). In a neutral atom the number of electrons equals the number of protons.

Atomic Structure and the Periodic Table (cont) Valence electrons are the electrons in the outer shell. The valence electrons determine which elements combine to form compounds!

Why do Elements Form Compounds? 1. Atoms combine to complete the outer energy shell of electrons 2. A complete outer energy shell is stable. (atoms with filled outer energy shells won’t combine with other atoms)

Why do Elements Form Compounds? 3. shell #1 it is complete with 2 electrons. 4. Shells # 2-7 are “complete” with 8 electrons

What happens when a chemical bond is formed? A chemical bond is the force of attraction that holds atoms together A new substance is formed in a chemical reaction properties of the new substance are different than the properties of the elements that make them up Electrons are gained, given away or shared

Electron Dot Diagrams Shows valence electrons only Uses dots to represent electrons Can be used to show how elements bond

Chemical Formula Chemical Formula - A shorthand way to write the name of the compound What information does a chemical formula contain?

Metals METALS are on the left side of the Periodic Table. They have a low number of valence electrons and can easily give them to other atoms. Almost empty shells

Nonmetals B. NONMETALS are on the right side of the Periodic Table. They have a high number of valence electrons and can easily take or share valence electrons from other atoms Almost full shells

Semi Metals C. SEMIMETALS are found between metals and nonmetals along the zigzag line. They can either lose or share valence electrons with other atoms About half full shell

Ionic Bonds ION- a charged particle; atoms either gain or lose electrons to form: A. Positive Ions form when atoms lose electrons (more protons than electrons) B. Negative Ions form when atoms gain electrons (more electrons than protons)

Ionic Bonds Metal to nonmetal Transfer of electrons from one atom to the other

How does an ionic bond form? 1.Metals lose electrons and form positive ions. Nonmetals gain electrons and form negative ions. 2. Ions with opposite charges attract each other (+ and – attract)

Properties of ionic compounds Very strong bonds Form crystal lattice (alternating, repeating) hard, brittle solids with high boiling and melting points, conduct electricity when dissolved in water.

Naming Ionic Compounds name the positive ion (metal) first name the negative ion (nonmetal) next with the ending changed to –ide NaCl: sodium + chlorine = sodium chloride

Name these: K2S: Potassium + sulfur = potassium sulfide Li2O: lithium + oxygen = lithium oxide Mg3P2 Magnesium + phosphorous = magnesium phosphide

Covalent bonds Form nonmetal to nonmetal Shared electrons

How does a covalent bond form? atoms share electrons to fill outer energy shells (it takes too much energy to transfer electrons) the force that holds atoms together in a covalent bond is the attraction of each atom’s nucleus for the shared pair of electrons

Properties of covalent compounds Weak bonds low melting & boiling points Many are gases and liquids cannot conduct electricity when dissolved in water

molecule a neutral group of atoms held together by a covalent bond; smallest piece of a compound Covalent compounds are also called molecular compounds

Diatomic Elements: An element that bonds with itself to form the simplest of molecules. There are only 7 elements that are diatomic. H, N, O, F, Cl, Br, I

Covalent bonds:

XI. Naming covalent compounds Use prefixes: Mono = 1 Di = 2 Tri = 3 Tetra = 4 Penta = 5 Hexa = 6

Carbon dioxide CO2 Carbon monoxide CO Dihydrogen monoxide H20

Metallic Bonds metal to metal Positive metal ions “swimming” in sea of released electrons

How does a metallic bond form? Metals tend to lose electrons and form positive ions. The bonds are held together by the force of attraction between positive metal ions and the many electrons surrounding them.

Metallic bond metal atoms combine in regular patterns which allow the electrons to move from atom to atom

Alloy mixture of 2 or more elements, at least 1 is a metal stronger and less reactive than pure metals. Properties of alloys are different from the pure metals that make them up

Metallic bond: mixture or chemical bond (honors slide) Alloys are a mixture because they can be in any ratio Alloys are like a chemical bond because they have different properties than the metals that form them Alloys are like a chemical bond because the electrons are interacting

Properties of Metals Dense shiny Solids at room temperature (except Mercury) malleable ductile Good conductors of heat and electricity

Number scratch paper from 1-10 Cross out number 8 Write the answer to fill in the blank