Presentation on theme: "SECTION 7.1 CHEMICAL NAMES AND FORMULAS Honors Chemistry."— Presentation transcript:
SECTION 7.1 CHEMICAL NAMES AND FORMULAS Honors Chemistry
Significance of a Chemical Formula A chemical formula indicates the relative number of atoms of each kind in a chemical compound. For a molecular compound, the chemical formula reveals the number of atoms of each element contained in a single molecule of the compound. example: octane — C 8 H 18 The subscript after the C indicates that there are 8 carbon atoms in the molecule. The subscript after the H indicates that there are 18 hydrogen atoms in the molecule.
Significance of a Chemical Formula The chemical formula for an ionic compound represents one formula unit—the simplest ratio of the compound’s positive ions (cations) and its negative ions (anions). example: aluminum sulfate — Al 2 (SO 4 ) 3 Parentheses surround the polyatomic ion to identify it as a unit. The subscript 3 refers to the unit. Note also that there is no subscript for sulfur: when there is no subscript next to an atom, the subscript is understood to be 1.
Reading Chemical Formulas Video
Monatomic Ions Many main-group elements can lose or gain electrons to form ions. Ions formed form a single atom are known as monatomic ions. example: To gain a noble-gas electron configuration, nitrogen gains three electrons to form N 3– ions. Some main-group elements tend to form covalent bonds instead of forming ions. examples: carbon and silicon
Monatomic Ions Naming Monatomic Ions Monatomic cations are identified simply by the element’s name. examples: K + is called the potassium cation Mg 2+ is called the magnesium cation For monatomic anions, the ending of the element’s name is dropped, and the ending -ide is added to the root name. examples: F – is called the fluoride anion N 3– is called the nitride anion
Common Monatomic Ions
Monatomic Charges Main Group Elements
Common Monatomic Ions d-Block and Group 14
Common Monatomic Ions Video
Naming Binary Compounds Binary Compounds contain only 2 elements. Binary Compounds ALWAYS end in –ide Exceptions Compounds with hydroxide - OH - Compounds with cyanide – CN - Compounds with peroxide – O 2 2-
Binary Ionic Compounds In a binary ionic compound, the total numbers of positive charges and negative charges must be equal. The formula for a binary ionic compound can be written given the identities of the compound’s ions. example: magnesium bromide Ions combined: Mg 2+, Br –, Br – Chemical formula: MgBr 2
Binary Ionic Compounds A general rule to use when determining the formula for a binary ionic compound is “crossing over” to balance charges between ions. example: aluminum oxide 1) Write the symbols for the ions. Al 3+ O 2– Cross over the charges by using the absolute value of each ion’s charge as the subscript for the other ion.
Practice Write formulas for the following: Magnesium and Iodine Potassium and sulfur Aluminum and chlorine Zinc and bromine Cesium and sulfur Strontium and oxygen Calcium and Nitrogen
Naming Ionic Compounds Video
Practice Name the following: BaF 2 CaO AgF CdO K 3 N NaI AlBr 3
Naming Ionic Compounds The Stock System of Nomenclature Some elements such as iron, form two or more cations with different charges. To distinguish the ions formed by such elements, scientists use the Stock system of nomenclature. The system uses a Roman numeral to indicate an ion’s charge. examples:Fe 2+ iron(II) Fe 3+ iron(III)
Naming Compounds Using the Stock System Video
Naming Compounds using the Classical System Ion with the higher charge uses –ic suffix. Ion with the lower charge uses the –ous suffix. Examples: CuCl 2 – cupric chloride CuCl – cuprous chloride SnO 2 – stannic oxide SnO – stannous oxide
Practice Write the formula and name for the following: Cu +, O 2- Fe 3+, S 2- Cu 2+, Cl - Sn 2+, Cl - Hg 2+, O 2- Sn 4+, S 2- V 2+, F - V 3+, Br -
Polyatomic Ions Many common polyatomic ions are oxyanions—polyatomic ions that contain oxygen. Some elements can combine with oxygen to form more than one type of oxyanion but always with the same charge. example: nitrogen can form: The name of the ion with the greater number of oxygen atoms ends in -ate. The name of the ion with the smaller number of oxygen atoms ends in -ite.
Polyatomic Ions Some elements can form more than two types of oxyanions. example: chlorine can form: In this case, an anion that has one fewer oxygen atom than the -ite anion has is given the prefix hypo-. An anion that has one more oxygen atom than the - ate anion has is given the prefix per-.
Naming Ternary Compounds (with Polyatomic Ions) Name the cation Name the anion The name of the polyatomic remains unchanged Name the salt Example - K 2 CO 3 Example - NH 4 OH
Understanding Formulas for Polyatomic Ionic Compounds
Naming Compounds Containing Polyatomic Ions Video
Practice Name the following: Ag 2 S NaMnO 4 Ba(OH) 2 Fe(ClO) 2 NH 4 NO 3 Ca(NO 3 ) 2 K 2 SO 3 NaCH 3 COO
Practice Write formulas for the following: Copper (II) nitrate Potassium iodide Sodium hydroxide Ammonium acetate Calcium carbonate Potassium permanganate Sodium sulfate Iron (III) nitrate
Naming Binary Molecular Compounds Unlike ionic compounds, molecular compounds are composed of individual covalently bonded units, or molecules. As with ionic compounds, there is also a Stock system for naming molecular compounds. The old system of naming molecular compounds is based on the use of prefixes. examples:CCl 4 — carbon tetrachloride (tetra- = 4) CO — carbon monoxide (mon- = 1) CO 2 — carbon dioxide (di- = 2)
Prefixes for Naming Covalent Compounds
Naming Binary Molecular Compounds Put the less electronegative element first. This element only has a prefix if there is more than one of the element. Name the second element – prefix/root/ide Drop o or a at the end of the prefix if the element begins with a vowel. Example – monoxide Example – VO 5 – vanadium pentoxide
Naming Compounds Using Numerical Prefixes Video
Naming Molecular Compounds Using the Stock System Write the names of the elements. After the first element add the apparent charge in parentheses written as a Roman Numeral. Example: CO – carbon monoxide or carbon (II) oxide CO 2 – carbon dioxide or carbon (IV) oxide P 2 O 3 – diphosphorous trioxide or phosphorous (III) oxide
Practice Name the following with prefixes and using the Stock System: PF 5 XeF 4 CCl 4
Practice Write the formulas for the following: Carbon dioxide Dinitrogen pentoxide Sulfur hexafluoride
Covalent-Network Compounds Some covalent compounds do not consist of individual molecules. Instead, each atom is joined to all its neighbors in a covalently bonded, three-dimensional network. Subscripts in a formula for covalent-network compound indicate smallest whole-number ratios of the atoms in the compound. examples:SiC, silicon carbide SiO 2, silicon dioxide Si 3 N 4, trisilicon tetranitride.
Acids and Salts An acid is a certain type of molecular compound. Generally we refer to solutions with available hydrogen ions (H + ) as acids. Most acids used in the laboratory are either binary acids or oxyacids. Binary acids are acids that consist of two elements, usually hydrogen and a halogen. Oxyacids are acids that contain hydrogen, oxygen, and a third element (usually a nonmetal).
Acids and Salts In the laboratory, the term acid usually refers to a solution in water of an acid compound rather than the acid itself. example: hydrochloric acid refers to a water solution of the molecular compound hydrogen chloride, HCl Many polyatomic ions are produced by the loss of hydrogen ions from oxyacids. examples: sulfuric acidH 2 SO 4 sulfate nitric acidHNO 3 nitrate phosphoric acidH 3 PO 4 phosphate
Acids and Salts An ionic compound composed of a cation and the anion from an acid is often referred to as a salt. examples: Table salt, NaCl, contains the anion from hydrochloric acid, HCl. Calcium sulfate, CaSO 4, is a salt containing the anion from sulfuric acid, H 2 SO 4. The bicarbonate ion,, comes from carbonic acid, H 2 CO 3.
Naming Acids Binary acids are named as follows: Use prefix hydro- End name in –ic Example – HCl – hydrochloric acid HBr – hydrobromic acid Oxyacids are named as follows: Name of polyatomic -ic suffix if more oxygens (-ate ending) - ous suffix if less oxygens (-ite ending) Example – H 2 SO 4 (from sulfate) – sulfuric acid Example – H 2 SO 3 (from sulfite) – sulfurous acid
Naming Binary Acids Video
Naming Oxyacids Video
Prefixes and Suffixes for Oxyanions and Related Acids Video
Compound’s Formula Metal/Nonmetal (2 elements) 2 Nonmetals IONIC COVALENT (Molecular Compounds) Cation (+) stays the same – use Roman Numeral if more than 1 charge possible Anion (-) changes to an –ide ending First nonmetal stays the same and uses prefixes if more than one Second nonmetal changes to an –ide ending and gets a prefix Metal/Polyatom ic (3 elements) Cation (+) stays the same – use Roman Numeral if more than 1 charge possible Polyatomic stays the same Polyatomic/Nonmetal (3 elements) Polyatomic stays the same Anion (-) changes to an –ide ending Uncross subscripts Check Charges
Compound’s Name Name has prefixes Use prefixes to write the formula for the compound COVALENT IONIC Write the symbols for each element or polyatomic Write the charges on each element or polyatomic (Roman Numeral = charge) Cross over |charges| Reduce subscripts if possible