Atom – the smallest unit of matter “indivisible”
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Atom the smallest unit of matter indivisible
HeliumatomValence ElectronsValence electrons are the electrons in the highest occupied energy level of the atom.
Valence electrons are the only electrons generally involved in bond formation. Electron Configuration of Sodium1s2 2s2 2p6 3s1
Which is the valence electron for Na?
Answer: 1s2 2s2 2p6 3s1
Na , 11 e
Na + , 10eelectron shellsAtomic number = number of Electrons
Electrons vary in the amount of energy they possess, and they occur at certain energy levels or electron shells.
Electron shells determine how an atom behaves when it encounters other atoms
Electrons are placed in shells according to rules: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 electronsC would like to N would like toO would like toGain 4 electronsGain 3 electronsGain 2 electronsWhy are electrons important?Elements have different electron configurationsdifferent electron configurations mean different levels of bonding
Electron Dot StructuresSymbols of atoms with dots to represent the valence-shell electrons
1 2 13 14 15 16 17 18H He: Li Be B C N O : F :Ne : Na Mg Al Si P S :Cl :Ar :
Electron Dot Structure or Lewis Dot Diagram A notation showing the valence electrons surrounding the atomic symbol.
Chemical bonds: an attempt to fill electron shellsIonic bonds Covalent bonds Metallic bondsLearning 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
IONIC BONDbond 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 gasPositive 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+When Na, (Z= 11) loses its valence electron, what element does its configuration look like ?NeonPotassium BerylliumSodiumCheck your Neighbor 18C. discover the property called inertia.
When the valence shell is full, the atom is stable, less likely to react.
Example: Noble (Inert Gases)KrA Stable Octet 19Formation of Sodium Ion Sodium atom Sodium ion Na e Na +
2-8-1 2-8 ( = Ne)
11 p+ 11 p+ 11 e- 10 e- 0 1+
Formation of Magnesium IonMagnesium atom Magnesium ion Mg 2e Mg2+ 2-8-2 2-8 (=Ne)
12 p+ 12 p+ 12 e- 10 e- 0 2+
Equations for the Formation of CationsH. H+ + e-
Li. Li+ + e-
Mg: Mg2+ + 2e-
Equations for the Formation of Anions . .. : F : + e- : F - : .. .. Some Typical Ions with Positive Charges (Cations)Group 1Group 2Group 13H+Mg2+Al3+Li+Ca2+Na+Sr2+K+Ba2+
Learning Check A. Number of valence electrons in aluminum1) 1 e- 2) 2 e-3) 3 e-
B. Change in electrons for octet1) lose 3e- 2) gain 3 e- 3) gain 5 e-
C.Ionic charge of aluminum 1) 3- 2) 5- 3) 3+ Solution A. Number of valence electrons in aluminum3) 3 e-
B. Change in electrons for octet1) lose 3e-
C.Ionic charge of aluminum 3) 3+ Learning CheckGive 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 CompoundsAre made up of:a metal and a nonmetal ion.polyatomic ions.
Ions from Nonmetal IonsIn 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 Ionunpaired electronoctet 1 - : F + e: F :
2-7 2-8 (= Ne) 9 p+ 9 p+ 9 e- 10 e- 0 1 - ionic chargeIonic BondBetween atoms of metals and nonmetals with very different electronegativityBond formed by transfer of electronsProduce 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.
Example:Which of the following compounds are ionic?
Some Common Ions
COVALENT BONDbond formed by the sharing of electrons
Covalent BondBetween nonmetallic elements of similar electronegativity.Formed by sharing electron pairsStable non-ionizing particles, they are not conductors at any stateExamples; O2, CO2, C2H6, H2O, SiC
Covalent BondsBonds in all the polyatomic ions and diatomics are all covalent bonds
when electrons are shared equallyNONPOLAR COVALENT BONDSH2 or Cl22. Covalent bonds- Two atoms share one or more pairs of outer-shell electrons.
Oxygen AtomOxygen Molecule (O2)
when electrons are shared but shared unequallyPOLAR COVALENT BONDSH2OPolar 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.
POLAR COVALENT BOND the electrons shared by the atoms spend a greater amount of time closer to one particular atomThis creates a partial negative end and a partial positive end
METALLIC BONDbond found in metals; holds metal atoms together very stronglyMetallic BondFormed between atoms of metallic elementsElectron cloud around atoms Good conductors at all states, lustrous, very high melting pointsExamples; 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.Chemical FormulaA representation of the kinds and number of atoms in a substance.Formula UnitA chemical formula that shows the lowest whole number ratio of the atoms (ions) in an ionic compound.
Example: KCl, Mg Cl2The formula unit is used because ionic compounds have a lattice arrangement of ions. Ex: NaClWhich ball represents the Na?
NUMBER OF BONDS BETWEEN ATOMS
Single bonds one pair of electrons; longest bond length; weakest bond
Cl Be Cl
Double bonds two pairs of electrons
Triple bonds three pairs of electrons; shortest bond length; strongest bondN NINTERMOLECULAR FORCES
London Dispersion Forces (Van der Waals Forces)1. weakest of all intermolecular forces2. the attractive or repulsive force between molecules (or between parts of the same molecule)
Dipole-Dipole Interactions1. between polar molecules
Hydrogen Bonds1. strongest of all intermolecular forces2. hydrogen bonded to a very electronegative atom (O,N,F)H FN NElectronegativity & Bond Type ElectronegativityBond TypeExample0.0-0.49Nonpolar covalentH-H (0.0)0.5-1.69Polar covalentH-Cl (0.9)>1.7IonicNa-Cl (2.1)VSEPRValence Shell Electron-Pair RepulsionA. predicts the shape of individual molecules based upon the extent of electron-pair electrostatic repulsionB. Double bonds count as one pair of electrons Bond Angle# atoms# e- pairs# unshared e- pairsExampleLinear180320BeCl2CO2Bent104.5342H2OTrigonal Pyrimidal107441NH3Tetrahedral109.5540CH4Trigonal Planar120430BF3
Trigonal Pyrimidal 107CH4
Trigonal Planar 120