Atomic Structure and the Periodic Table
• Review the structure of the atom• Protons?• Neutrons?• Electrons?• Nucleus?• Electron Cloud?
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?
1. A chemical bond is the force of attraction that holds atoms together
2. A new substance is formed in a chemical reaction
3. properties of the new substance are different than the properties of the elements that make them up
4. 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)
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
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
XI. Naming covalent compounds
• Use prefixes:
• Mono = 1
• Di = 2
• Tri = 3
• Tetra = 4
• Penta = 5• Hexa = 6
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