Atom the smallest unit of matter indivisible Helium
Atom the smallest unit of matter indivisible Helium atom electron shells a) Atomic number = number of Electrons 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 Gain 4 electrons N would like to Gain 3 electrons O would like to Gain 2 electrons Why are electrons important? 1) Elements have different electron configurations different electron configurations mean different levels of bonding Electron Dot Structures
Symbols of atoms with dots to represent the valenceshell electrons 1 2 13 14 15
16 17 18 H He:
Li Be B
C Na Mg
Si : F :Ne :
S :Cl :Ar :
Chemical bonds: an attempt to fill electron shells 1. Ionic bonds 2. Covalent bonds 3. Metallic bonds Learning Check A.
X would be the electron dot formula for 1) Na B. X
1) B 2) K 3) Al would be the electron dot formula 2) N 3) P
IONIC BOND bond formed between two ions by the transfer of electrons 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+ Formation of Sodium Ion Sodium atom
Na 2-8-1 11 p+ 11 e0 e Sodium ion
Na + 2-8 ( = Ne) 11 p+ 10 e1+ Formation of Magnesium Ion Magnesium atom Magnesium ion
Mg 2-8-2 12 p+ 12 e0 2e
Mg2+ 2-8 (=Ne) 12 p+ 10 e2+ Some Typical Ions with Positive Charges (Cations) Group 1 Group 2
Group 13 H+ Mg2+ Al3+ Li+ Ca2+
Na+ Sr2+ K+ Ba2+ Learning Check A. Number of valence electrons in aluminum
1) 1 e2) 2 e3) 3 eB. C. Change in electrons for octet 1) lose 3e2) gain 3 eIonic charge of aluminum 1) 32) 5- 3) gain 5 e- 3) 3+
Solution A. Number of valence electrons in aluminum 3) 3 eB. Change in electrons for octet 1) lose 3e- C.
Ionic charge of aluminum 3) 3+ Learning Check Give the ionic charge for each of the following: A. 12 p+ and 10 e1) 0 2) 2+ 3) 2B. 50p+ and 46 e1) 2+ 2) 4+
3) 4- C. 15 p+ and 18e2) 3+ 2) 3- 3) 5- 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- Fluoride Ion unpaired electron :F
2-7 9 p+ 9 e0 octet + e
1- : F: 2-8 (= Ne) 9 p+ 10 e1ionic charge 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, CaCl2, K2O Ionic Bonds: One Big Greedy Thief Dog! 1). Ionic bond electron from Na is transferred to Cl, this causes a charge imbalance in each atom. The Na becomes (Na+) and the Cl becomes (Cl-), charged
particles or ions. COVALENT BOND bond formed by the sharing of electrons Covalent Bond Between nonmetallic elements of similar electronegativity. Formed by sharing electron pairs Stable non-ionizing particles, they are not
conductors at any state Examples; O2, CO2, C2H6, H2O, SiC Bonds in all the polyatomic ions and diatomics are all covalent bonds NONPOLAR COVALENT BONDS
when electrons are shared equally H2 or Cl2 2. Covalent bonds- Two atoms share one or more pairs of outer-shell electrons. Oxygen Atom
Oxygen Atom Oxygen Molecule (O2) POLAR COVALENT BONDS when electrons are shared but shared unequally
H2O Polar Covalent Bonds: Unevenly matched, but willing to share. - water is a polar molecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen. METALLIC BOND bond found in
metals; holds metal atoms together very strongly Metallic Bond Formed between atoms of metallic elements Electron cloud around atoms Good conductors at all states, lustrous, very high melting points Examples; Na, Fe, Al, Au, Co
Metallic Bonds: Mellow dogs with plenty of bones to go around. Ionic Bond, A Sea of Electrons Metals Form Alloys Metals do not combine with metals. They form Alloys which is a solution of a metal in a metal. Examples are steel, brass, bronze and pewter. Formula Weights
Formula weight is the sum of the atomic masses. Example- CO2 Mass, C + O + O 12.011 + 15.994 + 15.994 43.999 Practice Compute the mass of the following compounds round to nearest tenth & state type of bond: NaCl;
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