Presentation on theme: "Bonding Ionic Valence Electrons The number of valence electrons in an atom of an element determines the many properties of that element, including the."— Presentation transcript:
Valence Electrons The number of valence electrons in an atom of an element determines the many properties of that element, including the ways in which the Atom can bond with other atoms
electron shells a)Atomic number = number of Electrons in a neutral atom b)Electrons vary in the amount of energy they possess, and they occur at certain energy levels or electron shells. c)Electron shells determine how an atom behaves when it encounters other atoms
Electrons are placed in shells according to rules: 1)The 1st shell can hold up to two electrons, and each shell thereafter can hold up to 8 electrons.
Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons C would like to N would like to O would like to Gain 4 electrons Gain 3 electrons Gain 2 electrons
Why are electrons important? 1)Elements have different electron configurations different electron configurations mean different levels of bonding As the number if protons (atomic number) increases, the number of electrons also increases. As a result, the properties of the elements change in a predictable way across a period.
Lewis Electron Dot Structures Symbols of atoms with dots to represent the valence-shell electrons 1 2 13 14 15 16 17 18 H He: Li Be B C N O : F : Ne : Na Mg Al Si P S : Cl : Ar :
Learning Check A. X would be the electron dot formula for 1) Na2) K3) Al B. X would be the electron dot formula 1) B2) N3) P
Chemical bonds: an attempt to fill electron shells 1.Ionic bonds 2.Covalent bonds 3.Metallic bonds
Ions and Ionic Bonds You and a friend walk past a market that sells apples for 40 cents each and pears for 50 cents each. You have 45 cents and want an apple. Your friend also has 45 cents but wants a pear.
Ions and Ionic Bonds When an atom loses an electron, it loses a negative charge and become a positive ion. When an atom gains an electron, it gains a negative charge and becomes a negative ion.
Ions and Ionic Bonds Ions are atoms that have lost or gained electrons. Ionic Bonds form as a result of the attraction between positive and negative ions
Some Typical Ions with Positive Charges (Cations) Group 1Group 2Group 13 H + Mg 2+ Al 3+ Li + Ca 2+ Na + Sr 2+ K + Ba 2+
Learning Check Give the ionic charge for each of the following: A. 12 p + and 10 e - 1) 02) 2+3) 2- B. 50p + and 46 e- 1) 2+2) 4+3) 4- C. 15 p + and 18e- 2) 3+ 2) 3-3) 5-
Ionic Bond Between atoms of metals and nonmetals with very different electronegativity Bond formed by transfer of electrons Produce charged ions all states. Conductors and have high melting point. Examples; NaCl, CaCl 2, K 2 O
Formation of Ions from Metals Ionic compounds result when metals react with nonmetals Metals lose electrons to match the number of valence electrons of their nearest noble gas Positive ions form when the number of electrons are less than the number of protons Group 1 metals ion 1+ Group 2 metals ion 2+ Group 13 metals ion 3+
Ions from Nonmetal Ions In ionic compounds, nonmetals in 15, 16, and 17 gain electrons from metals Nonmetal add electrons to achieve the octet arrangement Nonmetal ionic charge: 3-, 2-, or 1-
2. Covalent bonds- Two atoms share one or more pairs of outer-shell electrons. Oxygen Atom Oxygen Molecule (O 2 ) Oxygen Molecule (O 2 )
Covalent Bond Between nonmetallic elements of similar electronegativity. (Between two nonmetals!) Formed by sharing electron pairs Stable, not conductors at any state Examples; O 2, CO 2, C 2 H 6, H 2 O, SiC
How Covalent Bonds Form The force that holds atoms together in a covalent bond is the attraction of each atom’s nucleus for the shared pair of electrons.
- Covalent Bonds How Covalent Bonds Form Covalent bonds usually form between atoms of nonmetals. CO 2 H 2 0 NH3
- Covalent Bonds How Covalent Bonds Form The oxygen atom in water and the nitrogen atom in ammonia are each surrounded by eight electrons as a result of sharing electrons with hydrogen atoms.
- Covalent Bonds How Covalent Bonds Form In covalent bonds, atoms share two or more pairs of electrons Except for hydrogen, the number of covalent bonds that nonmetal atoms can form equal the number of electrons needed to make a total of 8 Hydrogen needs only two.
- Covalent Bonds How Covalent Bonds Form Covalent bonds can be double or triple bonds Double bonds refer to two pairs of shared electrons. Triple bonds include three shared electrons
- Covalent Bonds How Covalent Bonds Form An oxygen molecule contains one double bond, while a carbon dioxide molecule has two double bonds. A nitrogen molecule contains one triple bond.
Equal and Unequal Sharing of Electrons Nonpolar bonds: Electrons are equally shared. Fluorine forms a nonpolar bond with another fluorine atom. Polar bonds: electrons are shared unequally In hydrogen fluoride, fluorine attracts electrons more strongly than hydrogen does, so the bond formed is polar.
Polar Covalent Bonds: Unevenly matched, but willing to share.
Equal and Unequal Sharing of Electrons A carbon dioxide molecule is a nonpolar molecule because of its straight-line shape. In contrast, a water molecule is a polar molecule because of its bent shape.
- water is a polar molecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen.
Molecular Compunds A molecular compound contains atoms that are covalently bonded Compared to ionic compounds, molecular compounds generally have lower melting and boiling points and do not conduct electricity when dissolved in water - Covalent Bonds
Comparing Molecular and Ionic Compounds The table compares the melting points and boiling points of a few molecular compounds and ionic compounds.. - Covalent Bonds
Comparing Molecular and Ionic Compounds Melting points of molecular compounds are lower than those of ionic compounds. Interpreting Data: Describe what the table reveals about the melting points of molecular compounds compared to those of ionic compounds. - Covalent Bonds
Comparing Molecular and Ionic Compounds Molecular compounds have weak attractive force between molecules, so less energy is needed to melt molecular compounds. Inferring: How can you account for the differences in melting points between molecular compounds and ionic compounds? - Covalent Bonds
Comparing Molecular and Ionic Compounds Boiling points of molecular compounds are lower than those of ionic compounds. Interpreting Data: How do the boiling points of the molecular and ionic compounds compare? - Covalent Bonds
Metals Form Alloys Metals do not combine with metals to form compounds. They form an alloy, which is a solution of a metal in a metal. Examples are steel, brass, bronze and pewter.\
Metals Form Alloys Properties of Alloys Conduct heat and electricity Malleable Ductile Have luster (shiny) Used in jewelry, mirrors, buildings, etc
Bonding Summary Ionic bonds – between metals and nonmetals Covalent bonds – between two nonmetals Metallic bonds – between metals
Graphic Organizer Attraction between oppositely charged ions FeatureIonic Bond Polar Covalent Bond Nonpolar Covalent Bond Metallic Bond How Bond Forms Charge on Bonded Atoms? Example Unequal sharing of electrons Yes; positive or negative Yes; positive O 2 molecule Equal sharing of electrons Attraction between positive ions and surrounding electrons. Yes, slightly positive or slightly negative No NaCl crystal (or other ionic compound) H 2 O molecule (or other polar covalent molecule) Calcium (or other metal)