Compound Names & Formulas

Compound Names & Formulas
1. Use the periodic table and a list of ions to convert names to formulas and formulas to names for : a) simple ionic compounds b) ionic compounds with multivalent metals c) ionic compounds with polyatomic ions 2. Convert names to formulas and formulas to names for covalent compounds, using prefixes up to “deca”

VOCABULARY Ionic compound Covalent compound Combining capacity Ion
Attract Repel Valence electrons Chemical bond Simple ionic bond Multivalent ions Polyatomic ions Molecules

Ionic compounds are made up of positive and negative ions. All of the positive and negative ions organize in a pattern. Negative-positive attract. Negative-negative and positive-positive repel. Salt, NaCl See pages (c) McGraw Hill Ryerson 2007

Ionic compounds form from the inside out as solid crystals. Ionic compounds are like a solid stack of bricks. A salt shaker contains thousands of small pieces of NaCl. See pages (c) McGraw Hill Ryerson 2007

Naming Simple Ionic Compounds
Compounds are usually named to show what elements have combined to make the compound. If a compound is formed from 2 elements then it is named by writing the 2 elements and then changing the name of the second one to “ide”. E.g. ~ NaCl is named as E.g. ~ KI is named as E.g. ~ Al2O3 is named as E.g. ~ Si3N4 is named Sodium chloride Potassium iodide Aluminum oxide Silicon nitride See pages (c) McGraw Hill Ryerson 2007

STEP 1: identify the two elements STEP 2: always write the metallic element first. STEP 3: change the ending of the 2nd element to “ide”. MgBr2 = NaCl = K2O = CaCl2 = Magnesium bromide Sodium chloride Potassium oxide Calcium chloride See pages (c) McGraw Hill Ryerson 2007

The name of an ionic compound = positive ion + negative ion-ide. Example, what is the name of Ca3N2? Ca, the positive ion, is calcium. N, the negative ion, is nitrogen. Drop the end of the anion and add -ide. Calcium nitride See pages (c) McGraw Hill Ryerson 2007

Writing Formulas for Simple Ionic Compounds
Atoms bond according to these rules: In a compound, every valence electron of an atom must be paired The valence shell becomes full

Example: Write the formula for Water Water is made up of Hydrogen (H) and Oxygen (O). Hydrogen has a combining capacity of +1, it has one valence electron. Oxygen has a combining capacity of -2, it wants two valence electrons.

Example: Write the formula for Water It takes two hydrogen atoms to fill the valence shell of one oxygen atom.

STEP ONE: Write the symbol for the more metallic element first. Then, write the symbol for the non-metallic element. STEP TWO: Write the combining capacities for the elements. Ignore the + and – charges. *If there is no #, the combining capacity is 1. STEP THREE: Criss cross the combining capacities to get the subscripts. Calcium chloride Ca 2 Cl 1 Ca1Cl2 CaCl2 REMEMBER: Subscripts indicate the number of atoms each element has in that compound. *If the element has only one atom, then no subscript is needed for that element.

STEP ONE: Write the symbol for the more metallic element first. Then, write the symbol for the non-metallic element. STEP TWO: Write the combining capacities for the elements. Ignore the + and – charges. *If there is no #, the combining capacity is 1. STEP THREE: Criss cross the combining capacities to get the subscripts. Lithium Nitride Li 1 N 3 Li3N1 Li3N REMEMBER: Subscripts indicate the number of atoms each element has in that compound. *If the element has only one atom, then no subscript is needed for that element.

STEP ONE: Write the symbol for the more metallic element first. Then, write the symbol for the non-metallic element. STEP TWO: Write the combining capacities for the elements. Ignore the + and – charges. *If there is no #, the combining capacity is 1. STEP THREE: Criss cross the combining capacities to get the subscripts. Barium Sulphide Ba 2 S 2 Ba2S2 BaS REMEMBER: In an ionic compound, the positive charges balance out the negative charges. The subscripts are always written in reduced form. So, divide the subscripts by their lowest common denominator.

STEP ONE: Write the symbol for the more metallic element first. Then, write the symbol for the non-metallic element. STEP TWO: Write the combining capacities for the elements. Ignore the + and – charges. *If there is no #, the combining capacity is 1. STEP THREE: Criss cross the combining capacities to get the subscripts. Calcium carbide Ca 2 C 4 Ca4C2 Ca2C REMEMBER: In an ionic compound, the positive charges balance out the negative charges. The subscripts are always written in reduced form. So, divide the subscripts by their lowest common denominator.

What is the formula for magnesium phosphide? magnesium is Mg2+ phosphorous is P3– Need 3 Mg2+ ions and 2 P3– ions Mg3P2 Calcium oxide, also known as “quicklime” was once produced by cooking limestone in ancient kilns. Try the formula for calcium oxide. calcium is Ca2+ oxygen is O2– Need 1 Ca2+ ion and 1 O2– ions Ca2O2, which is simplified and written as CaO See page 188 (c) McGraw Hill Ryerson 2007

Names & Formulas for Multivalent Ionic Compounds
Some elements have more than one combining capacity (MULTIVALENT), so elements can combine in more than one way. The most common c.c. is listed on top. Iron can have a combining capacity of 2 or 3: Example 1: Sometimes when iron combines with oxygen, it can act like it has a combining capacity of 2 and form a black compound (FeO = Iron II oxide) Example 2: Sometimes when iron combines with oxygen, it can act like it has a combining capacity of 3 and form a rust-coloured compound (Fe2O3 = Iron III oxide) See pages (c) McGraw Hill Ryerson 2007

If an atom has only one possible combining capacity (like sodium, zinc, or aluminum), a roman numeral is not written after its name. E.g. Sodium Chloride = E.g. Zinc Sulphide = E.g. Aluminum oxide = A roman numeral is written after the name of an element with more than one combining capacity so that chemists know which form of the element we are dealing with. E.g. Iron II chloride = E.g. Copper I oxide = E.g. Nickel III bromide = E.g. Titanium IV oxide = NaCl ZnS Al2O3 FeCl2 Cu2O NiBr3 TiO See pages

It is easy to write the formulas for multivalent ionic compounds, because they tell you their combining capacities so you don’t need to look on the periodic table. Example: Gold (I) chloride: Au+1 Cl-1 AuCl Iron (III) sulphide: Fe+3S-2 Fe2S3 Lead (IV) oxide: Pb+4O-2 Pb2O4 PbO2 See pages

It is a little more difficult to name a multivalent ionic compound, because you have to work backwards to figure out which combining capacity was used. Remember to use a ROMAN NUMERAL!!! Example: SnCl Sn = tin Cl = chloride 2. Combining capacity of tin is either 4 or +2 3. Combining capacity of chlorine is -1 4. Reverse the combining capacities to figure out which combining capacity was used. 5. Ask yourself, is “2” an option? If the answer is yes, you can name the compound: Tin (II) chloride Sn Cl 1 2

Example: PbO 1. Pb = lead O = oxide 2. Combining capacity of lead is +2 or +4 3. Combining capacity of oxygen is -2 4. Reverse the combining capacities to figure out which combining capacity was used. 5. Ask yourself “is 1 an option?” 6. If the answer is “no”, then check if the numbers were reduced. In this case, oxygen is 2, and if it has been reduced to “1”, then both subscripts must have been divided by 2. 7. So, do the opposite and multiply by 2. 8. Now you can name the compound: Lead (II) oxide 2 2 Pb O 1 1

Example: CuCl Cu = copper Cl = chloride 2. Combining capacity of copper is +1 or +2 3. Combining capacity of chlorine is -1 4. Reverse the combining capacities to figure out which combining capacity was used. 5. Ask yourself “is 2 an option?” 6. If the answer is “yes”, then you can name the compound: Copper (II) chloride Cu Cl 1 2

Write the formula for Manganese (III) sulfide. This manganese is Mn3+ sulfur is S2– Mn2S3 Write the name for TiF4 titanium is Ti4+ or Ti3+ fluorine is F– 1 Ti4+ ion and 4 F– ions titanium (IV) fluoride See pages (c) McGraw Hill Ryerson 2007

Names & Formulas for Ionic Compounds with Polyatomic Ions
Some ions, called polyatomic ions, are made up of several atoms joined together with covalent bonds. The whole group has a + or – charge, not the individual atoms. See pages (c) McGraw Hill Ryerson 2007

The groups of atoms have their own combining capacity that should be used when writing chemical formulas. USE BRACKETS AROUND THE POLYATOMIC IONS!! Example: Compound formed with Na and CO3 would be… Example: Compound formed between Ca and OH would be… +1 Na (CO3) -2 Na 2(CO3) +2 -1 Ca (OH) Ca(OH)2 See pages (c) McGraw Hill Ryerson 2007

When you are naming compounds with more than two elements, you are dealing with a polyatomic ion. All you need to do, is find it in the chart so you can name your compound. If the polyatomic ion group has a positive charge (+) it acts like a metal and comes first in the name. If the polyatomic ion group has a negative charge (-) it acts like a non-metal and comes second in the name. Example: Na2 CO3 = 3 different elements Does Sodium carbon oxide sound right? No!! You must have a polyatomic ion. See chart. Name: sodium carbonate See pages (c) McGraw Hill Ryerson 2007

Example 2: Ca (OH)2 = 3 different elements Does calcium oxygen hydride sound right? No!! You must have a polyatomic ion. See chart. Name: Calcium hydroxide Example 3: NaNO3 = 3 different elements Does Sodium nitrogen oxide sound right? No!! You must have a polyatomic ion. See chart! Name: Sodium Nitrate Example 4: NH4Cl = 4 different elements Does Nitrogen hydrogen chloride sound right? No!! Name: ammonium chloride See pages (c) McGraw Hill Ryerson 2007

What is the formula of sodium sulphate? Na+ and SO42– Na2SO4 What is the name of the compound KClO? K+ = potassium ClO– = hypochlorite potassium hypochlorite

Covalent molecules share electrons. Covalent bonds occur between two or more non-metals. These molecules exist as solids, liquids or gases. Covalent molecules are like a play-pit full of plastic balls. Each plastic ball = covalent molecule of H2O Water, H2O See pages (c) McGraw Hill Ryerson 2007

The chemical formula of a covalent compound tells us the number of each element in the compound. Sometimes the names don’t tell us what elements make up the compounds. Subscripts mean something different in covalent compounds Ionic compounds subscripts show the smallest whole-number ratio between the ions in the compound. Covalent molecules have subscripts that show the actual number of atoms in the molecule. Water: H2O Hydrogen Peroxide: H2O2 See page 193 (c) McGraw Hill Ryerson 2007 Methane: CH4

What is the chemical formula for the molecule ethanol? C2H6O, a name that must be memorized or looked up when needed. What is the chemical formula for candle wax? C25H52 What is the name of the molecule C12O22H11? Sucrose, also called table sugar. (c) McGraw Hill Ryerson 2007 See page 193

Covalent compounds with 2 non-metal atoms use a system of prefixes. Prefixes are often used before the atom name to indicate the number of atoms in the molecule. Example: CO = carbon monoxide CO2 = carbon dioxide CCl4 = carbon tetrachloride See pages (c) McGraw Hill Ryerson 2007

STEP 1: Write the most metallic atom (farthest left) first STEP 2: Use prefixes to symbolize the # of each atom. STEP 3: Add -ide to the end of the second atom’s name See pages (c) McGraw Hill Ryerson 2007

What is the chemical formula for the molecule trinitrogen tetrachloride? N3Cl4 What is the name of the molecule Si3P6? Trisilicon hexaphosphide See pages (c) McGraw Hill Ryerson 2007

How do you decide: Ionic or Covalent?
To determine whether a compound is ionic or covalent: Examine the formula. Does it start with a metal? It must be an Ionic compound. Does it start with the ammonium ion (NH4)? It must be an ionic compound with a polyatomic ion. Does it start with a non-metal? It must be a covalent compound. See pages (c) McGraw Hill Ryerson 2007

To determine whether a compound is ionic or covalent: If the compound is ionic: Check the metal to see if it has more than 2 combining capacities. It is does, follow the rules for a multivalent ionic compound. Don’t forget the Roman numerals when naming. Check to see if there are more than 2 elements in the compound. If there are, follow the rules for a polyatomic ionic compound. Don’t forget the brackets when writing the formula! Naming starts with the name of the metal atom (positive ion). If it ends with a single non-metal, naming will just end in -ide. If it ends in a polyatomic ion, look up the name/formula. See pages (c) McGraw Hill Ryerson 2007

To determine whether a compound is ionic or covalent: If the compound is covalent: Use the prefix system of naming If there are more than two different non-metal elements, or it starts with H, there is probably a different name for the covalent molecule. See pages (c) McGraw Hill Ryerson 2007

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Compound Names & Formulas

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