UNIT: Nomenclature Objectives: Lesson 2 of 3 You will learn what a Covalent Compound is You will learn how to write the formulas and names for Covalent Compounds You will learn and hopefully memorize the most common polyatomic ions You will also learn how to write formulas and names of polyatomic compounds TOPIC: Covalent and Polyatomic Compounds

Quickwrite In 1-2 sentences answer one of the questions below: Consider the Compound CO 2, how is this compound different from NaCl (hint: look at their location on the periodic table)??? Why do you think we use prefixes such as “tri-” on words like triceratops, tricycle or tripod?

Covalent Compounds Earlier we learned about Ionic Compounds which form between cations (usually metals) and anions (usually a non- metals) Covalent Compounds form when two or more non-metal elements share electrons Recall that Hydrogen is classified as a non-metal on the periodic table The simplest covalent compound is Hydrogen gas or H 2 Notice, that the electrons are not transferred, BUT, instead, they are shared between the two atoms As a result, Covalent Compounds DO NOT have charges like Ionic Compounds Therefore, we use a completely different naming system when writing their chemical formulas and names H 2 - Covalent Compound Cations (usually metals) Anions (usually non-metals)

What is a Covalent Compound? A compound formed between two non-metals that involves the sharing of electrons Example: CO, Carbon Monoxide

When naming covalent compounds there are certain steps you must follow These steps will help you throughout this unit and the rest of the course: 1.The first element in the formula is named first, and the full element name is used 2. The 2 nd element is named as though it were an anion (add –ide) 3. Prefixes (mono- 1, di- 2, tri- 3) are used to denote the numbers of atoms 4. The prefix mono- is never used for naming the first element

Prefixes di- (two) CO 2 - carbon dioxide tri- (three) N 2 O 3 - dinitrogen trioxide tetra- (four) CCl 4 - carbon tetrachloride Prefix Example mono- (one)CO - carbon monoxide penta- (five) N 2 O 5 - dinitrogen pentoxide hexa- (six) UF 6 - uranium hexafluoride

CO - Carbon Monoxide Write the name for the covalent compound CO - Carbon Monoxide 1. The first element in the formula is named first, and the full element name is used For Example: we just say “Carbon” for Carbon Monoxide 2. The 2 nd element is named as though it were an anion For Example: the Oxygen in CO is oxide 3. Prefixes are used to denote the numbers of atoms- For Example: Since there is 1 oxygen atom we would use the prefix mono- for Monoxide 4. The prefix mono- is never used for naming the first element For Example: CO is called Carbon Monoxide NOT Monocarbon Monoxide

SO 3 Sulfur Trioxide Write the name for the covalent compound SO 3 Sulfur Trioxide 1. The first element in the formula is named first, and the full element name is used SulfurSulfurTrioxide For Example: we just say “Sulfur” for Sulfur Trioxide 2. The 2 nd element is named as though it were an anion SO 3 For Example: the Oxygen in SO 3 is oxide 3. Prefixes are used to denote the numbers of atoms- Trioxide For Example: Since there are 3 oxygen atoms we would use the prefix tri- for Trioxide 4. The prefix mono- is never used for naming the first element SO 3 Sulfur Trioxide Monosulfur Trioxide For Example: SO 3 is called Sulfur Trioxide NOT Monosulfur Trioxide

N 2 O 5 - Dinitrogen Pentaoxide Write the name for the covalent compound N 2 O 5 - Dinitrogen Pentaoxide 1. The first element in the formula is named first, and the full element name is used For Example: we just say “Nitrogen” for Dinitrogen Pentaoxide 2. The 2 nd element is named as though it were an anion For Example: the Oxygen in N 2 O 5 is oxide 3. Prefixes are used to denote the numbers of atoms- For Example: there are 5 oxygen atoms so we would use the prefix penta- for Pentaoxide 4. The prefix mono- is never used for naming the first element For Example: Since their are 2 nitrogen atoms, we use the prefix di- for Dinitrogen

1. The first element in the formula is named first, and the full element name is used 2. The 2 nd element is named as though it were an anion 3. Prefixes are used to denote the numbers of atoms- mono- 1, di- 2, tri- 3, tetra- 4, penta- 5, hexa The prefix mono- is never used for naming the first element

Practice: names Write the names for the following compounds below: 1)SF 6 2)PCl 5 3)N 2 O 4 4)CCl 4 5)CO 2 6)NO 2 Sulfur Hexafluoride Answer: Sulfur Hexafluoride Phosphorous Pentachloride Answer: Phosphorous Pentachloride Dinitrogen Tetraoxide Answer: Dinitrogen Tetraoxide Carbon Tetrachloride Answer: Carbon Tetrachloride Carbon Dioxide Answer: Carbon Dioxide Nitrogen Dioxide Answer: Nitrogen Dioxide

Practice: formulas Write the formulas for the following compounds below: 1)Dinitrogen Dioxide 2)Sulfur Trioxide 3)Diphosphorous Pentaoxide 4)Nitrogen Monoxide 5)Carbon Tetrafluoride 6)Silcon Dioxide N 2 O 2 Answer: N 2 O 2 SO 3 Answer: SO 3 P 2 O 5 Answer: P 2 O 5 NO Answer: NO CF 4 Answer: CF 4 SiO 2 Answer: SiO 2

Polyatomic Ions [ ] +

Polyatomic Ions Common Polyatomic Ions: NameFormulaNameFormula nitrateNO 3 -1 chromateCrO 4 -2 chlorateClO 3 -1 phospitePO 3 -3 sulfateSO 4 -2 phosphatePO 4 -3 carbonateCO 3 -2 acetateC 2 H 3 O 2 -1 hydroxideOH -1 cyanideCN -1 ammoniumNH 4 +1 sulfite SO 3 -2

What are Polyatomic Ions? A group of two or more atoms that have a particular charge to them No naming rules exist, you must memorize their names and charge Polyatomic Ions you must memorize: NameFormulaNameFormula nitrateNO 3 -1 chromateCrO 4 -2 chlorateClO 3 -1 phospitePO 3 -3 sulfateSO 4 -2 phosphatePO 4 -3 carbonateCO 3 -2 acetateC 2 H 3 O 2 -1 hydroxideOH -1 cyanideCN -1 ammoniumNH 4 +1 sulfite SO 3 -2

Practice: formula and charge Write the formula and charge for each polyatomic ion below: 1)hydroxide 2)nitrate 3)phosphate 4)sulfate : OH - Answer: OH - NO 3 - Answer: NO 3 - PO 4 -3 Answer: PO 4 -3 : SO 4 -2 Answer: SO 4 -2

Ionic Compounds with Polyatomic Ions Naming ionic compounds that contain polyatomic ions is very similar to naming ionic compounds For example, the compound NaOH contains the cation, Sodium (Na +1 ) and the polyatomic ion hydroxide (OH -1 ) Remember, when Ionic compounds come together, their charges must always be neutral or ZERO Just like ionic compounds, we write the cation first and the anion second; giving us the compound Sodium Hydroxide--NaOH

Ionic Compounds with Polyatomic Ions Let us look at the compound ammonium nitrate NH 4 NO 3 (a very explosive chemical) Ammonium Nitrate is made up of 2 polyatomic ions Ammonium (NH 4 + ) & Nitrate (NO 3 - ) When two polyatomic ions come together, a neutral compound NH 4 NO 3 forms between them Notice, the cation is named first, and anion second

Ionic Compounds with Polyatomic Ions Consider Silver (I) Nitrate: AgNO 3 The Silver (Ag +1 ) cation comes first, and the polyatomic anion Nitrate (NO 3 -1 ) comes second Just like in ionic compounds, the charges need to be neutral The Silver cation Ag + with a plus one charge is balanced by the negatively charged polyatomic ion NO 3 -1 with a negative one charge It is important to realize that because Silver (Ag) is a transition metal it takes on multiple charges, therefore we still use roman numerals to illustrate charge Therefore we write: Silver (I) Nitrate

Ionic Compounds with Polyatomic Ions Consider one more compound: Mg(OH) 2 The Mg +2 cation comes first, and the negative polyatomic OH - anion comes second Just like in ionic compounds, the charges need to be neutral Mg +2 needs be balanced by 2 negatively charged polyatomic ions OH - In the case of Mg(OH) 2 when more than one polyatomic ion exists, we put PARENTHESIS around them By putting parenthesis around (OH) 2 and a subscript of 2, this tells us we have 2 oxygen atoms and 2 hydrogen atoms ( )

What are Ionic Compounds with Polyatomic Ions? Neutrally charged Compounds that contain a polyatomic ion When more than one polyatomic ion exists in a compound we put parenthesis around them Ex: Mg(OH) 2 & AgNO 3

Practice: names Write the names for the following compounds below: 1)NaOH 2)Ba(OH) 2 3)NH 4 Cl 4)AgNO 3 5)CaCO 3 6)Mg(NO 3 ) 2 Sodium Hydroxide Answer: Sodium Hydroxide Ammonium Chloride Answer: Ammonium Chloride Barium Hydroxide Answer: Barium Hydroxide Silver (I) Nitrate Answer: Silver (I) Nitrate Calcium Carbonate Answer: Calcium Carbonate Magnesium Nitrate Answer: Magnesium Nitrate For assistance, look back at the rules for naming Ionic Compounds

Practice: formulas Write the formulas for the following compounds below: 1)Calcium Hydroxide 2)Magnesium Sulfate 3)Aluminum Phosphate 4) Ammonium Hydroxide 5) Iron (II) Sulfate 6) Calcium Phosphate Ca(OH) 2 Answer: Ca(OH) 2 MgSO 4 Answer: MgSO 4 AlPO 4 Answer: AlPO 4 : NH 4 OH Answer: NH 4 OH FeSO 4 Answer: FeSO 4 Ca 3 (PO 4 ) 2 Answer: Ca 3 (PO 4 ) 2 For assistance, look back at the rules for naming Ionic Compounds

Summarize: (you can always write you own) Explain the difference between a Ionic Compound and a Covalent Compound: What numbers do the following prefixes represent: tetra-, tri-, penta-, hexa- Write down the polyatomic ions you need to memorize, arrange them in order according to their charge: Explain how we name polyatomic compounds: Explain how we write formulas for polyatomic compounds: What do we do if more than one polyatomic ion is present in a compound?