Naming Compound (Nomenclature)
Elements found in nature are not always in their pure form.
Elements in nature are actually in the form called ions .
Atoms that are electrically charged through the loss or gain of electrons
If it's a positive charge (+) It has lost an electron
If it's a negative charge (-) It has gained an electron
- Because elements are in an ion form, they are not stable (due to being electrically charged) but want to become stable (like the noble gases)
- By combining with another ion(s), they work together to become stable compounds
Two or more different elements chemically combined I.e. two or more atoms combine
Because of hundreds of years of chemistry, compounds have been studied and chemicals have been named according to the scientist. Until the 18th century, no standardized system existed for naming chemicals.
- 1787- Guyton do Morveau- used the chemical name for each element in the compound. He decided metal element names came first
- 1920- IUPAC (International Union of Pure & Applied Chemistry) is now responsible for naming all chemical compounds discovered
Naming Chemical Compounds
3 Things to Know About Chemical Names and Formulas:
1. Chemical formula - identifies what element(s) and how much of each element are in the formula
- Ex. NaCl: 1 atom of sodium and 1 atom of chlorine
2. Subscript Numbers - indicates the number of atoms of elements that must combine to form the compound. It is placed after the symbol and down
- Ex. H₂O or C₆H₁₂O₆
3. Indicating Physical State of Element or Compound. After the chemical formula, as subscripts put: (s) for a solid compound, (l) for a liquid compound, (g) for a gaseous compound, (aq) compound dissolved in water
- C₆H₁₂O₆ ₍s₎ or H₂O₍ʟ₎
These are atoms of the same element that have different numbers of neutrons in the nucleus. Their mass numbers will be different but atomic number is the same.
- Carbon 12- atu
- Carbon-14 used for carbon dating
- Oxygen-18 used to find pathways of photosynthesis
Pure substances in unique crystal formation formed as an attraction between particles of opposite charges
Positive ions attracted to negative charged ions
Negative ions attracted to positive charged ions
Forming Ionic Compounds
Metals bond to a non-metal !
K+ and Br- form KBr
Na+ and Cl - form NaCl
2 types of ions
A single atom that has a positive or negative electrostatic charge (ex. Ba+ or I-)
A group of atoms that behaves as a single unit with a positive or negative electrostatic charge (ex. NO3 ⁻ (nitrate))
NOTE: The charges are placed in a post superscript position!!
Ionic Characteristics :
- Solid at room temperature
- High melting point
- Good electrical conductor in aqueous solution
Ionic Charge Patterns:
- Earth metals (Group 1) have 1+ charge
- Alkaline Earth metals (Group 2) have a 2+ charge
- Halogens (Group 17) have a 1- charge
- Group 16 have a 2- charge
Naming Ionic Compounds
1. The chemical name of the metal (cation) comes first followed by the name of the non-metal (anion), but no charges are shown.
- Ex. CaO is calcium oxide
2. Name of the non-metal (anion) changes to an ‘ide’ suffix.
- Ex. Al2O3- aluminum oxide
3. If an element like copper (1+ or 2+) is used, add a Roman Numeral (I) or (II) after the word.
- Ex. Copper (II) Sulfate is CuSO4
Writing Ionic Compound Formulas
ALWAYS have a copy of the Periodic Table
1. Print the metal element’s symbol with its ion charge, next to it, print the non-metal element’s symbol with its ion charge.
- Ex: Ca2+ Cl1-
2. Balance the ion charges, the positive ion charge must balance the negative ion charges
- Ex: Ca2+ Cl1- Cl1-
In the example, this means that there must be two chlorine atoms each with an ion charge of 1- to balance the 2+ ion charge of one calcium atom.
3. Write the formula by indicating how many atoms of each element are in it.
- Do not include the ion charge in the formula!
- Place the number of atoms of each element in a subscript after the element’s symbol.
- If there is only one atom, no number is used
The Criss Cross Method!
When non-metals combine and consists of one or more non-metallic atoms. Ex. CO
- Differ from ionic compounds:
- Can be solids, liquids, or gases at room temp.
- Poor electrical conductors
- Low melting and boiling points
- All molecular elements are non metallic
Writing Molecular Compound Formulas
Similar to writing ionic compounds except:
- No ions are present
- Ion charge not used in the formulas
Formula will show: What elements are present & proportion of atoms in a molecule
- Ex. O₂₍g₎ has 2 oxygen atoms
IUPAC recommends that molecular compounds should be named using the prefix system only.
In the prefix system, Greek or Roman prefixes are used to indicate the number of each kind of atom bonded to one another
- The first element in the formula should be named in full.
- The second element in the formula should be shortened and given an ‘ide’ suffix…just like ionic compounds!
- When there is more than one atom in the formula, a prefix is used which specifies the number of atoms.
- The prefix ‘mono’ may be omitted on the first element
You heard of polyatomic, you heard of monatomic. Diatomic atoms are consisting of two atoms. Heteronuclear are two different elements ex. HBr, CO. All halogens are diatomic, as well as N, and O.
Recall: Evidence of a Chemical Rxn
- Color change, Odor, Gas or solid formation, release (exothermic) or absorption (endothermic) of heat
- Caution: be careful in the interpretation of the above criteria, ex. Bubbles could mean boiling or some solids release heat when dissolved
Chemical Reactions :
When two or more ionic or molecular substances combine to form new substances
- Example: Space Shuttle Launch: Oxygen (air) + Hydrogen (fuel) to drinking water
- In other words…. A chemical change occurs when atoms are rearranged. New substances with new properties form because the molecules, crystals, or networks that are formed by the change are different from those present before the change occurred.
We can express chemical reactions in 3 different ways…
- Chemical reaction: combustion of coal (mainly carbon)
- Word Equation: carbon + oxygen gas → carbon dioxide
- Formula Equation: C + O₂ → CO₂
- Reactants: materials at the start of a reaction
- Products: new materials produced by the reaction
- ‘+’ signs separate reactants and products
- ‘arrow’ indicate direction of reaction
- A + B → C + D
- (Reactants) → (Products)
- Paper + oxygen → Carbon dioxide + water
- In Other Words… All the facts about a chemical reaction can be expressed by means of a shorthand statement called a word equation.
- Ex. Photosynthesis: carbon dioxide + water + energy → glucose + oxygen
- The arrow is read as “yields”,“gives” or “reacts to produce”.
- The names of the reactants are written on the left of the arrow with plus signs between them. The names of the products are written on the right
- Ex. Photosynthesis: carbon dioxide + water + energy → glucose + oxygen
Reactions that release heat.
Ex. Burning of methane or wood releases energy in the form of heat and light
Reactions that absorb energy. Needs a continuous supply of energy .
Ex. A cold pack is triggered by a chemical reaction that absorbs heat from its surrounding.
Changes Involving Oxygen
- Combustion – oxygen reacts with a substance to produce a new substance plus heat
- Wood + oxygen → heat + light + exothermic energy
- All combustion is exothermic
- Corrosion (rusting)- a slow chemical change involving oxygen with some metals
- Iron + oxygen → rusted iron
- Cellular respiration- occurs in all aerobic (oxygen) consumers
- Food + oxygen →carbon dioxide + water + energy
Conservation of Mass in Chemical Reactions
Law of Conservation:
Matter and mass cannot be destroyed but can change form in a ‘closed’ controlled laboratory system
Reactants → Products
100 g → 100 g
Mg + S → MgS
24.3g + 32.1 g → 56.4 g
Matter is not created nor destroyed during a chemical rxn. However, this being said, some matter such as gases may and usually escape and not be accountably measured in an ‘open system’ reaction as performed in most school labs
What is a System?
An experiment in which all reactants and all products of a chemical reaction are accounted for
An experiment in which the exchange of matter as well as energy interacts with the surroundings
All chemical reactions must be balanced—the number of atoms, moles, and ultimately the total mass must be conserved during a chemical process.
1. Count the number of atoms on both the reactants and product sides of the equation
2. Using coefficients, balance the number of atoms. Always leave diatoms such as hydrogen and oxygen last
3. Check your work by counting the number of atoms on each side of the equation
Factors Affecting Rate of Chemical Reactions
4 Types of Factors:
A substance added to a reaction.
- To speed it up but it is not in itself used up or destroyed during the rxn…can be used over and over again & not consumed in the reactants. Ex. Enzymes are organic catalysts used extensively in the digestive system of the human body to break down various food groups and materials fig
2. Concentration of reactants
- The greater the concentration, the faster the reaction. Why? More atoms to react with each other
3. Temperature of the reactants
- Higher the heat, faster the reaction. Why? Causes the atoms to move faster creating more collisions with each other
4. Surface area of reactants
- Greater surface area (ex. Powder vs chunks) the more surface area will be available for the reaction. To occur, the faster the reaction will occur. Why? More surface area means that more area is available in relation to the volume for reaction.