Presentation on theme: " A chemical formula is a combination of symbols that represents the composition of a compound. Chemical symbols are used to indicate types of elements."— Presentation transcript:
A chemical formula is a combination of symbols that represents the composition of a compound. Chemical symbols are used to indicate types of elements present. Subscripts are used to indicate the number of atoms for each element present. Coefficients are used to indicate the total number of molecules present.
chemical symbols C 8 H 18 number of atoms of each element 8 atoms of carbon 18 atoms of hydrogen Total # of atoms (8 + 18 = 26)
chemical symbols 2C 8 H 18 number of atoms of each element 16 atoms of carbon (2x8) 36 atoms of hydrogen (2x18) Total # of atoms (16 + 36 = 52) # of molecules present
Nomenclature is defined as a naming system. Chemistry uses nomenclature to standardize names of chemicals. Let’s take a look.
Taurine - The stimulant in the 'energy drink' Red Bull
Remember: Molecules are substances that are covalently bonded together. They contain a nonmetal bonded to a nonmetal. How can you tell the difference between a polyatomic ion and a molecule? Ions have a charge when not bonded to a metal – ex. (PO 4 ) 3- or K 3 PO 4 Molecules contain only nonmetals and NO overall charge – ex. P 2 O 3
1 mono-6 hexa- 2 di-7 hepta- 3 tri-8 octa- 4 tetra-9 nona- 5 penta-10 deca- In order to be effective in naming molecules, these prefixes must be committed to memory:
FIRST WORD/ELEMENT: NAME OF ELEMENT THAT APPEARS FIRST IN FORMULA PREFIX TO SHOW # ATOMS IF “ONE/MONO”– NO PREFIX SECOND WORD/ELEMENT: PREFIX TO SHOW # ATOMS “STEM” OF SECOND ELEMENT + “IDE” Example: Chlorine Choride
NOTE: The o or a at the end of a prefix is usually dropped when the word following the prefix begins with another vowel. EX: monoxide or pentoxide instead of monooxide or pentaoxide
PCl 3 Phosphorous trichloride Cl 2 O 7 Dichlorine heptoxide CO Carbon monoxide
EX: SO 3 is ____________________ Sulfur trioxide PBr 5 is ____________________ Phosphorus pentabromide ICl 3 is _____________________ Iodine trichloride H 2 0 is _____________________ Dihydrogen monoxide
Now… let’s look at writing the molecular formula from the name. 1. Write the Symbol for the first element with the atom’s prefix as its subscript. (Reminder: if NO prefix, don’t write subscript – understood to be ONE (1)) 2. Write the symbol for the second element with the atom’s prefix as its subscript. Let’s view some examples…
Example #1- Names to Formulas Sulfur trioxide S O 3 2. Write number of atoms 1. Write symbols of elements Final Formula If no prefix, then 1 is implied and not written
Example #2- Names to Formulas dichlorine heptoxide Cl O 2 7 2. Write number of atoms 1. Write symbols of elements Final Formula
Example #3- Names to Formulas phosphorus pentachloride P Cl 5 2. Write number of atoms 1. Write symbols of elements Final Formula If no prefix, then 1 is implied and not written
Example #4- Names to Formulas di nitrogen monoxide N O 2 2. Write number of atoms 1. Write symbols of elements Final Formula If no prefix, then 1 is implied and not written
Example #5- Names to Formulas carbon monoxide C O 2. Write number of atoms 1. Write symbols of elements Final Formula If no prefix, then 1 is implied and not written
Example #6- Names to Formulas dinitrogen trisulfide N S 2 3 2. Write number of atoms 1. Write symbols of elements Final Formula
Learning Check….. Nitrogen dioxide NO 2 Sulfur hexafluoride SF 6 Tetraiodine nonoxide I4O9I4O9
Diatomic Molecules All bonds in diatomic molecules are covalent bonds
1. Molecule – two or more atoms covalently bound together 2. Diatomic Molecule – two of the same atom bound together. Br, I, N, Cl, H, O, F They are called the BIG SEVEN Color these on your periodic table These atoms do NOT exist alone because they are extremely reactive. They always come in pairs.
TWO TYPES OF IONS: MONATOMIC: CATION (+) OR ANION (-) DERIVED FROM A SINGLE ATOM EXAMPLES: Al +3, Cl -1, Mg +2, O -2 POLYATOMIC: CATION (+) OR ANION (-) DERIVED FROM A GROUP ATOMS EXAMPLES: NH 4 +3, NO 3 -1, CO 3 -2
The charge on a monatomic ion is the same thing as its oxidation number. Because atoms want to reach an octet of valence electrons, the oxidation numbers, positive or negative charges, can be predicted for single atoms (monatomic). Metals tend to have positive oxidation numbers. (lose e-) Nonmetals tend to have negative oxidations numbers. (gain e-)
Predicting Charges on Monatomic Ions KNOW THESE !!!! +1 +2 +3 X -3 -2 -1 0 Cd +2 Write these on your periodic table!
Group 1: Lose 1 electron to form 1+ ions H+H+H+H+ Li + Na + K+K+K+K+
Group 2: Loses 2 electrons to form 2+ ions Be 2+ Mg 2+ Ca 2+ Sr 2+ Ba 2+
Group 13: Loses 3 electrons to form 3+ ions B 3+ Al 3+ Ga 3+
Group 14: Lose 4 electrons or gain 4 electrons? Neither! Group 14 elements rarely form ions (Except Sn and Pb which act like transition metals.)
Group 15: Gains 3 electrons to form 3- ions Gains 3 electrons to form 3- ions N 3- P 3- As 3- Nitride Phosphide Arsenide
Group 16: Gains 2 electrons to form 2- ions O 2- S 2- Se 2- Oxide Sulfide Selenide
Group 17: Gains 1 electron to form 1- ions F 1- Cl 1- Br 1- Fluoride Chloride Bromide I 1- Iodide
Groups 3 - 12: Some transition elements Some transition elements have only one possible oxidation state. have only one possible oxidation state. Zinc = Zn 2+ Silver = Ag +
Groups 3 - 12: Many transition elements Many transition elements have more than one possible oxidation state. Iron(II) = Fe 2+ Iron(III) = Fe 3+
The oxidation number of a transition element can be determined by: The Roman Numeral indicating the oxidation. EX: iron (II) is Fe +2 iron (III) is Fe +3
Cations 1 oxidation # Anions 1 oxidation # Transition Elements More than 1 oxidation # Common cations and anions *put on periodic table
Polyatomic ions are ions that are made up of two or more atoms. Refer to table of Polyatomic ions. Polyatomic ions generally have the following endings: “ate” or “ite” EX: NO 2 - nitrite PO 4 -3 phosphate
Ionic Compounds always made up of: Positively Charged Ion + Negatively Charged Ion CATION+ ANION An ionic compound MUST be NEUTRAL: Total positive charge = total negative charge
1. Determine cation – write symbol and charge. (Positive charge – usually a metal) 2. Determine anion – write symbol and charge. (Negative charge – non-metal or polyatomic) 3. Write cation first, anion second. 4. Determine ratio of cation (+) to anion (-) to make compound neutral (equal (+) and (-). Shortcut = criss-cross. 5. Use subscripts to denote ratio of ions (use parentheses if more than one polyatomic ion needed.) If “1” – do NOT write subscript. 6. Make sure subscripts of final compound are in LOWEST WHOLE NUMBER RATIO. 7. Check – final compound should have NO charges in it.
Determine cation and anion. Cation first, anion second. Write the name of the cation: If ion can have multiple charges (i.e. transition metals), indicate charge with Roman Numeral Write the name of the anion: Monatomic – stem of element + “ide” Polyatomic – write name of polyatomic ion
1. Simple binary ionic with monatomic ions. 2. Transition Metals - cations with multiple charges. 3. Ternary ionic compounds – binary ionic compounds with polyatomic ions.
USING STEPS TO DETERMINE FORMULA FOR COMPOUND BETWEEN OF POTASSIUM AND IODINE. 1. Determine cation – write symbol and charge. (Positive charge – usually metal) POTASSIUM K + 2. Determine anion – write symbol and charge. IODINE I -
3. Write cation first, anion second. K + I - 4. Determine ratio of cation (+) to anion (-) to make compound neutral (equal (+) and (-). Shortcut = criss-cross. 1 K + : 1 I -
5. Use subscripts to denote ratio of ions (use parentheses if more than one polyatomic ion needed.) If “1”, do NOT write subscript. KI 6. Make sure subscripts of final compound are in LOWEST WHOLE NUMBER RATIO. 7. Check – final compound should have NO charges in it.
Same process as writing simple ionic formulas: Write cation – symbol and charge Write anion – symbol and charge Balance and use subscripts to write final formula (criss-cross) Examples: Lead (II) chloride Tin (IV sulfide
If cation is a transition metal – it MAY have more than one charge (remember: Ag, Zn and Cd only have one ) Use formula to determine WHICH charge is on the cation for THAT formula Can sometimes reverse criss cross Determine from anion Write name of transition metal with Roman Numeral in parentheses Pb +1 Lead (I) Sn +4 Lead (IV) Write anion as before – stem + “ide”
Same Process!!! Write cation – symbol/formula and charge Write anion – symbol/formula and charge Criss cross/Balance using subscripts If more than one polyatomic ion needed, use parentheses (subscript outside!)
Now, let’s include polyatomic ions. EX: Calcium Nitrate Ca +2 NO 3 -1 Formula: Ca(NO 3 ) 2
Learning Check…… Write the formulas for the following: Potassium nitrite Magnesium sulfate Ammonium chloride Sodium carbonate
Ternary Compounds contain a polyatomic ion. 1. Write name of cation as it is on the periodic table. 2. Write the name of the poly-atomic ion as it is written on the sheet. Don’t change the ending! EX: Al 2 (SO 4 ) 3 Aluminum sulfate EX: Mg(OH) 2 Magnesium hydroxide
Same as all other ionics!!! Name cation If polyatomic – just write name of polyatomic Name anion If polyatomic – just write name of polyatomic – do NOT change to “ide” Example: