Presentation on theme: "Valence electrons w Electrons in the highest occupied energy level of an atom. w These are the electrons that determine the elements properties."— Presentation transcript:
Valence electrons w Electrons in the highest occupied energy level of an atom. w These are the electrons that determine the elements properties.
Electron dot structures w Diagrams that show the valence electrons as dots. w The core electrons and the nucleus are included in the symbol of the element
Octet Rule w In forming compounds, atoms tend to achieve noble gas configuration. w 8 electrons in the highest energy level.
IONS w Atoms or groups of atoms that have a positive or negative charge. w Cations - positive ion resulting from loss of electrons. w Anions - negative ions resulting from gain of electrons.
Formula Unit w Represents an ionic compound. w Lowest whole number ratio of ions in the compound.
Formula units Ionic compounds form as repeating links in a crystal matrix. Each cation is bound to each neighboring anion The ions are locked in place NaCl is the smallest ratio that indicates this matrix
Ionic Bond w Bonds resulting from the electrostatic attraction between oppositely charged ions. In an ionic compound the net ionic charge is 0.
Ionic Compounds w Metal + Non-metal w Polyatomic cation+Non-metal w Metal+ Polyatomic anion w Solid at room temperature w High melting point >300°C
Ionic compounds NaCl Na 2 SO 4 CaCO 3 1. Crystalline solids that have high melting points. 2. They are often soluble in water 3. They conduct electricity when in solution, or when molten.
Predicting the formula 1. Identify the charge of the cation 2. Identify the charge of the anion 3. Make a T table 4. Add ions until the positive charge equals the negative charge
Predicting the formula Polyatomic ions are groups of atoms that stay together, they are treated like super atoms The entire group carries the charge. Table 9.3 p.257 NH4+NH4+ NH4+NH4+
Lets Review!!! calcium chlorideCaCl 2 cesium oxideCs 2 O aluminum perchlorateAl (ClO 4 ) 3 barium sulfideBaS sodium dichromateNa 2 Cr 2 O 7 aluminum phosphateAl PO 4 calcium carbonateCaCO 3 sodium carbonateNa 2 CO 3
Compounds with transition metals Transition metals can have more than one charge. You may have more than one possible compound: FeO, or Fe 2 O 3 Make tables & work backwards to determine cation charge Indicate charge with a roman numeral REMEMBER THE TABLE MUST BE BALANCED !!!!! Fe +? O -2 Fe +? O -2 Fe +? O -2 iron(II) oxide iron(III) oxide
Some Ions we need to just Know w Silver is always +1 w Zinc is always +2 w Cadmium is always +2 w Do not use a roman numeral with these w Iron may be +2 or +3 w Tin may be +2 or +4 w Lead may be +2 or +4 w More in table 9.2 p.255
Lets Practice calcium carbonateCaCO 3 ammonium sulfate(NH 4 ) 2 SO 4 copper(I) phosphateCu 3 PO 4 chromium(IV) acetateCr(C 2 H 3 O 2 ) 4 cadmium perchlorateCd(ClO 4 ) 2
Links to practice tests and games w Interactive link Interactive link w Interactive link 2 Interactive link 2 w Interactive link 3 Interactive link 3 w Interactive link 4 Interactive link 4
Metallic Bonds w The force of attraction that holds metals together. The attraction of the free floating electrons for the positively charged metal ions
Metallic Properties w Malleable w Ductile w Conduct heat and electricity.
Single covalent bond w A bond in which two atoms share a pair of electrons between them in order to achieve noble gas configuration.
Structural formulas w Chemical formulas that show the arrangement of atoms in molecules and polyatomic ions. Each dash represents a pair of shared electrons.
Unshared pairs w Pairs of valence electrons that are not involved in bonding, not shared between atoms. w Also called lone pairs or non-bonding pairs
Double covalent bond w Two atoms share two pairs of electrons between them to attain noble gas configuration. w O 2 and CO 2
Triple covalent bond w Two atoms share three pairs of electrons between them to attain noble gas configuration. wN2wN2
Coordinate covalent bond w A covalent bond in which one atom contributes both bonding electrons. w CO and NH 4 + and N 2 O
Exceptions to the octet rule w NO 2 w BF 3 w PCl 5 w SF 6
Law of Definite Proportions w In samples of any chemical compound, the masses of the elements are always in the same proportions.
Law of Multiple Proportions w When two elements form more than one compound, the different masses of one element that combine with the same mass of the other element are in the ratio of small whole numbers.
Isoelectronic ions w Ions containing the same numbers of electrons. w Generally for isoelectronic ions size decreases as nuclear charge increases.
Bond energy w The energy required to break a bond. w Table 8.4 p.365 w Bond length- the distance where energy is minimum.Table 8.5 p.365
Coulombs Law w E=2.31x Jxnm Q 1 Q 2 w r w E= energy in joules w r= distance between ion centers in nm w Q 1 &Q 2 = ion charges
Molecular Compounds w All non-metals covalently bonded. w Solid, liquid or gas w Low melting point <300°C w Smallest representative particle is a molecule.
Non-polar covalent bond w A covalent bond in which the electrons are shared equally. The two atoms have nearly the same electronegativities
Polar covalent bond w A covalent bond in which the electrons are not shared equally. The more electronegative atom will pull more of the electrons toward itself.
Polar molecule w One end of the molecule has a slightly positive charge and one has a slightly negative charge. w This is called a dipole. w Depends on the shape.
Lattice energy w The change in energy that takes place when separated gaseous ions are packed together to form an ionic solid. w Lattice Energy=k(Q 1 Q 2 ) w r
Use the following to calculate H° f of BaCl 2(s). w Lattice energy= kJ/mol w 1st ionization Ba= 503kJ/mol w 2nd ionization Ba= 965kJ/mol w Electron affinity Cl=-348kJ/mol w Bond energy Cl 2 =239kJ/mol H sublimation Ba=178kJ/mol
Bond Energies & Enthalpy H= D(bonds broken)- D(bonds formed) =sum of terms w D=bond energy per mol of bonds, always positive.
Localized Electron Bonding Model w A molecule is composed of atoms that are bound together by sharing pairs of electrons using the atomic orbitals of the bound atoms. w Lewis Structures w VSEPR Theory
Writing Lewis Structures w Sum the valence electrons from all the atoms. w Use a line to show a pair of electrons between each pair of bound atoms. (Bonding Pairs)
Writing Lewis Structures w Arrange the remaining electrons to satisfy the duet rule for hydrogen and the octet rule for the 2nd row elements. (Lone Pairs) w Double or triple bonds may be needed.
Comments on Octet Rule w C,N,O,F obey octet rule. w B and Be often have less than 8 electrons. Very reactive. w 2nd row never exceed rule. w 3rd row and up often obey octet rule but may exceed it., due to d orbitals.
w When writing lewis structures satisfy the octet rule for the atoms first. Place any remaining electrons on the elements that have available d orbitals.
Resonance structures w Occur when it is possible to have two or more valid electron dot structures for the same molecule or ion. w SO 3, SO 2
Formal Charge (FC) w A method to decide which of many possible non- equivalent Lewis structures is most likely to occur. w Atoms in molecules try to achieve FC as close to 0 as possible.
w FC=(# valence e - on free atom) -(# valence e - assigned to the atom in the molecule). w (Valence e - ) assigned = (# lone pair electrons) + 1/2(#shared electrons)
VSEPR theory w Valence-shell-electron-pair repulsion theory. w Because electron pairs repel molecular shape adjusts so the valence electron pairs are as far apart as possible.
Hybrid orbitals w In hybridization several atomic orbitals mix to form the same number of equivalent hybrid orbitals
Sigma bonds w Formed along the axis that joins the atomic nuclei when two atomic nuclei combine to form a molecular orbital.
Pi bond w Electron in pi bonds are found in sausage shaped regions above and below, or in front and behind the bond axis.
Paramagnetic molecules w Show an attraction to an external magnetic field. w Molecules contain one or more unpaired electrons.
Diamagnetic Molecules w Molecule is repelled by an external magnetic force. w Associated with paired electrons
Electronegativity w The ability of an atom in a compound to draw electrons to itself. w Pauling electonegativity values Table 14.2 p.405 w Large electronegativity differences correspond to ionic bonds