chemical formulas and bonding ions and molecules
Embed Size (px)
CHEMICAL FORMULAS AND
BONDING Ions and Molecules
➢Understand octet rule and how it applies to oxidation state of an ion.
➢What do all atoms need in order to be stable?
➢ Elements will gain or lose electrons in order to obtain a noble gas valence (full shell)
➢ It takes energy to gain or lose electrons➢ Nature wants to move towards the path of
……because it requires less energy
Gain or Lose Electrons?
➢ Depends on the nearest noble gas.
➢ Oxygen has 6 valence electrons➢ Is it easier to gain 2e- or lose 6e-?➢ Easier to gain 2e-
➢ Sodium has 1 valence e-
➢ Is it easier to gain 7e- or lose 1e-?➢ Easier to lose 1e-.
➢ Sulfur➢ Fluorine➢ Potassium➢ Argon➢ Carbon➢ Hydrogen➢ Calcium
➢ The possible charge an atom could obtain by gaining or losing electrons or the number of electrons an element will donate/accept in a bond.
● Remember electrons are negative
➢ Oxygen gains 2e-
● So its charge is 2-
➢ Sodium loses 1e-
● So its charge is 1+
➢ Magnesium➢ Boron➢ Bromine
Loses 2e-, Mg2+
Loses 3e-, B3+
Gains 1e-, Br-
2 TYPES OF CHEMICAL BONDS WE WILL TALK ABOUT
➢Ionic compounds ➢Covalent compounds
➢2 terms that go with the ionic and covalent:➢Empirical➢Molecular
1. What is the oxidation number for Rubidium? Selenium?
2. Do metals have (+) or (–) oxidation numbers?
3. Do non metals have (+) or (–) oxidation numbers?
Review1. What rule states that elements will gain or lose electrons to obtain a noble gas valence?
o Octet Rule
2. Do non metals have (+) or (–) oxidation numbers?
3. Do metals have (+) or (–) oxidation numbers?• (+)
5. What is the oxidation number for barium? Iodine?
➢ Ba2+ and I-
Goal of Today
➢Know how to write formulas for Ionic Compounds.
➢ Electrons are everywhere – static is a good example
➢ Positive ion is attracted to a negative ion in an ionic bond
➢ What kind of elements?
➢ Made up of ions➢ Electrically neutral➢ Charges must equal each other➢ Bonds between metals (+ charge) and
nonmetals (- charge)
Ionic Bonding➢ Ionic bonds occur
between positive metal ions (cations) and negative nonmetal ions (anions)
➢ Made up of ions➢ Electrically neutral➢ Charges must equal
Properties of Ionic Compounds
➢ Strong bonds➢ High melting points➢ Brittle➢ Soluble in water➢ Their solutions are
good conductors of electricity
➢ Solids at 20°C
Formation of Ionic Compounds
➢ Use ● The Octet rule● Lewis Dot Diagrams● Crisscross Method
➢ Positive 1, 2, or 3➢ Transition metals can vary, and even have
a charge of 4+➢ Use element name➢ Use a Roman numeral with any metal that
varies in charge➢ Example Copper(I) is Cu+1 and Copper (II)
➢ Can be negative 1,2, or 3➢ Change element name to “-ide” ending➢ Example: chloride
➢ Two or more atoms that are bonded together and carry a single charge
➢ Names are on the handout➢ Most are negative with one positive➢ Usually end in “-ate” or “-ite”➢ Example: NO3
- is nitrate
Formulas for Binary Compounds
➢ Contain a monatomic cation (metal) and a monatomic anion (nonmetal)
➢ Metal is first➢ Charges must add to “0”➢ Use subscripts to get the value to “0”➢ Why is sodium chloride NaCl?➢ Try some
Write the formulas for the following
➢chromium (III) sulfide
➢gold (III) bisulfate
1. What are negative ions called?
2. What are positive ions called?
3. Write the formula for niobium(V) phosphate
Goal of Today
➢Understanding naming of Ionic Compounds and begin our “Ionic Bonding Puzzle Lab”
Naming Ionic Compounds
➢ Use NaCl as a good example➢ Metal first, then nonmetal➢ Ends in “-ide” if binary (2 elements only)➢ Use polyatomic name➢ Use Roman numeral if necessary➢ Suspect every transition metal to possibly
have a Roman numeral
1. Write the formulas for:beryllium carbonatesilver nitrate
2. Name the following ionic compound:Cu(HSO4)2
GOAL OF TODAY
Understand how covalent bonds form and know how to draw Lewis structures to represent covalent compounds.
➢ A covalent bond is formed by a shared pair of electrons between two atoms.
➢ A group of atoms that are united by covalent bonds is called a MOLECULE
➢ Most of what you see is covalently bonded
Describing a molecular bond
➢ Molecular formula: tells you how many atoms and which kind are in each molecule. Glucose C6H12O6
➢ Empirical formula: gives you the ratio of the atoms in a molecule. Glucose: C1H2O1
➢ Single bonds share 2 electrons. Example:
Ammonia (H-N-H) H
➢ Double bonds share 4 electrons:
H ➢ Triple bonds share 6
1.What is the difference between ionic bonds and covalent bonds?
2.Draw the Lewis structure for N2H2
GOAL OF TODAY
➢Know that there are exceptions to the octet rule.
➢Know how to determine and notate polarity of chemical bonds.
Exceptions to the Octet Rule
➢ Some elements are satisfied with fewer than 8 electrons (6 or 4)
➢ Some structures can only be drawn with 7 electrons
➢ Compounds with Beryllium (Be) and Boron (B) may have less than an octet BCl3
➢ 3rd Row elements or lower may exceed octet rule. SF4.
➢ Odd number of electrons cannot follow the octet rule. I.e., NO or CO
➢ These substances can be short-lived and reactive – called free radicals
Draw the Lewis structure for chloroform
➢Draw the Lewis structure for PF3
Properties of Covalent Bonds
➢ Electrons are not necessarily shared equally. This depends on the electronegativity of an atom (atom’s attraction for electrons)
Polar and Nonpolar Covalent Bonds
➢ Polar bonds: 1 atom is significantly more electronegative than the other one. One side of the bond is slightly positive the other negative. Example: Water
➢ Nonpolar bonds: Both atoms have similar electronegativities. Example:
Bond Type by Electronegativity
➢ First, Find the difference of electronegativities of the atoms.Then apply the information of the table below
< 0.4 Non-polar covalent
Between 0.4 and 2.0 Polar covalent
> 2.0 Ionic bond
Goal for Today
➢Review bond polarity➢Know the difference in naming ionic and covalent compounds.
Look at the table on page 241.
➢ What is the electronegativity difference between hydrogen and oxygen (H20)?
● 1.4 (polar covalent)➢ What is the electronegativity difference
between sodium and chlorine (NaCl)?● 2.1 approximately (ionic)
➢ What is the electronegativity difference between 2 nitrogen atoms (N2)?
● 0 (non polar covalent)
Properties of Molecular Substances
• Weak bonds
• Can be solids, liquids, or gases at 20°C
• Lower melting points
• Poor conductors of electricity
• Soft, not hard and brittle
• Some are soluble in water.
Naming Molecular Compounds
• Similar to naming ions• Numerical prefixes are used. Example:
CO2=Carbon Dioxide• Do not use a prefix for one• - ide is added to the more electronegative
element• Some elements have common names: Diatomics like O2= oxygen; not dioxide NH3= ammonia; not Nitrogen tetrahydride
H2O is water not dihydrogen monoxide
Ionic compounds that absorb water into their solid structures.
CuSO4. 5 H2O (s)
Copper (II) Sulfate pentahydrate