Chapter 2: Names, Formulas and Properties

2.1: CHEMICAL NAMES AND FORMULAS

• All Scientists use an international system for naming chemicals that is maintained by the International Union of Pure and Applied Chemistry (IUPAC)

• Each pure substance has a single, unique name called its systematic name

• A pure substance’s systematic name describes its composition and enables us to write its composition and predict some of its properties

BINARY COMPOUNDS

• Binary compounds are made up of two elements only. Binary compounds can be either molecular or ionic, depending on the bonds that exist in the compound.

• Binary Molecular Compounds: Compounds with two elements joined by covalent bonds.

  • The first Element in the name and in the formula is usually the element that is farther to the left on the periodic table (ie CO₂)

  • The suffix ‘-ide’ is attached to the name of the second element 

  • Prefixes indicate how many atoms of each type are present in one molecule of the compound

  • **no ‘mono’ prefix on solo first elements

BINARY COMPOUNDS

• Binary Ionic Compounds: Two elements (a metal and a non-metal) joined by ionic bonds.

  • The first element in the name and in the formula is the metal

  • The second element, the non metal, is named as an ion (‘-ide’ is attached to the name

  • The chemical formula shows the simplest whole-number ratio of each type of ion in the compound

**since ionic compounds form crystal lattices, their formulas do not represent molecules. They represent the smallest repeating unit in the lattice. The name for these units is formula units

Names of ionic compounds DO NOT contain prefixes. Therefore, to determine the formula for the compound, you balance your electrons to decide how many of each type of element will be present

CATION CHARGES

• Atoms of some elements (for example the transition metals) can form more than one ion. Your periodic table will provide the possible ionic charges. In order to determine which one is involved in your reaction, determine which ion will result in an overall neutral charge for the formula unit:

• Atoms with more than one possible ion charge are called Multivalent.
  

• Naming Cations Using the Stock System 

  • In the Stock System (named for a German Chemist) the charge of the cation is written in parentheses as a roman numeral after the name of the metal.

    • Ex: Cu⁺ is called Copper(I) and Cu²⁺ is called Copper(II)

  • The names of cations that use the Stock system tell us right away which cation to use when multiple cations are possible. 

    • Ex:  Iron(II) Oxide

This system is used only for metals that have more than one type of cation (transition metals).

COMPOUNDS CONTAINING POLYATOMIC IONS

These compounds are not binary because one or both ions are made up of more than one element.

• Polyatomic ions are made of one or more different atoms that are joined by covalent bonds that have an overall positive or negative charge as a group

  • Ex: NH₄⁺, SO₄^2-

• Many common polyatomic ions are negatively charged, and have the suffix ‘-ate’. We are given a list of common polyatomic ions and their names on our periodic tables

• Compounds containing Polyatomic ions are classified as ionic. We name them by naming the cation followed by the name of the anion

• We use parentheses in the formulas for Polyatomic ions when more than one of an ion is present. ex:  Al(NO₃)₃

FAMILIES OF POLYATOMIC IONS

Many polyatomic ions are composed of oxygen and one other non-metallic element (ex. Nitrate NO₃^- and Sulfate SO₄^2-). Many of these ions have ‘relatives’ that contain the same elements and have the same charge (ex. Nitrite NO₂^- and Sulfite SO₃^2-)

• In each family, the anion ending with ‘-ate’ is the reference point. The other anions are named according to the number of oxygen atoms in their formula in relation to that reference point.

• ‘-ite’ anions have one less oxygen atom than the reference ‘-ate’ anion

• ‘Hypo_____ite’ anions have two less oxygen atoms than the reference ‘-ate’ anion

• Per________ate anions have one more oxygen atom than the reference ‘-ate’ anions

HYDROGEN COMPOUNDS

Hydrogen is a non-metal, and most compounds whose names begin with hydrogen are molecular

• Even though they are molecular, the names of hydrogen-containing substances do NOT contain prefixes (Ex: the correct name for HCl is hydrogen chloride not hydrogen monochloride and the correct name for H₂S is hydrogen sulfide, not dihydrogen monosulfide)

Substances containing Carbon and Hydrogen like C₆H₁₂O₆ have their own set of naming rules that you will learn in subsequent science courses.

RULES FOR NAMING ACIDS:

• Names for many acidic solutions come from the compounds found in the solution.

• Hydrogen _____ide solutions are named hydro______ic acid

• For acids composed of hydrogen and a polyatomic ion (see next slide for examples):

  • Hydrogen ____ate solutions are named ________ic acid

  • Hydrogen ____ite solutions are named _______ous acid

  • ***you have an acids naming chart on the back of your periodic table. Use it.

  • It is also correct to name an acid as an aqueous solution (ex – hydrosulfuric acid H₂S_(aq) can also be called aqueous hydrogen sulfide

    RULES FOR NAMING BASES

Bases are simply ionic compounds made from a metal and polyatomic ion! No new rules here, name as you would for ionic compounds

EXPLAINING PROPERTIES OF SUBSTANCES

Chemists use subscripts to show the state that a substance is in, because substances have different properties in different states (s – solid, l – liquid, g – gas, aq – aqueous)

• Properties of Ionic compounds:

  • Made from a cation and an anion with an ionic bond between atoms in which the metals are transferring electrons to the anion

  • Regular, crystaline shape when solid (because of crystal lattice)

  • Tend to have high melting points

  • Non – conductive when solid because ions are ‘trapped’ in the lattice and not free to move

  • Forms an electrolyte when melted or dissolved in water – conduct electricity well. This happens once the ions can move freely once out of the crystal lattice
    

• Properties of Molecular Compounds

  
  Made up of all non-metals in which covalent bonds are formed between atoms where electrons are shared

• Most have fairly low melting points

• Once melted, can usually be melted further without decomposing into other compounds or elements

• Tend to be non-electrolytes (do not conduct electricity in any state as pure substances)

• Most do not conduct electricity when dissolved in water (but some do). Further testing is required if something conducts electricity when dissolved in water

SOLUBILITY 

Solubility is the ability of a compound to be dissolved in some solvent.

• When an ionic compound is soluble in water it dissolves to form ions and becomes aqueous. 

• Temperature and pressure both effect the solubility

  • As temperature rises the solubility rises

  • As pressure rises the solubility rises

  • A compound that is not soluble at room temperature could become soluble if the temperature is high enough

• Non-soluble compounds that form from a reaction are called precipitates

PROPERTIES OF ACIDS AND BASES

• Acids:

  • A substance that releases hydrogen ions (H⁺_(aq)) in a water solution

Ex: HCl_(g) in water forms H⁺_(aq) and Cl^-_(aq)

• Very important and common group of chemicals with useful properties:

  • Provide the tangy flavour of fruits and some other foods due to their sour taste (***NEVER taste anything in a science classroom unless you are specifically told to!)

  • Used to remove rust and refine and process metals among many other commercial and common uses.

  • Strong acids can be dangerous and must be handled with care

• Bases

  • A substance that releases hydroxide (OH^-_(aq)) ions when dissolved in water

Ex:  NaOH_(s) when dissolved in water produces Na⁺_(aq) and OH^-_(aq) ions

• Bitter tasting

• Have a slippery feel

• Often used in cleaning products

• Corrosive, so must be handled with care

INDICATORS AND PH

• Acid-base indicators are chemicals that change colour in response to the concentration of hydrogen or hydroxide ions in a solution

• Litmus and Phenolpthalein are common indicators
  

USING COMMON INDICATORS

Phenolthalien is colourless in acids, and turns bright pink in bases.

• Litmus is red in acids and blue in bases
  

• Bromethymol blue is yellow in acids, green when neutral, and blue in base

• Universal Indicator changes colour at specific pH values and can be matched to a spectrum.

• Chemists use the pH scale to talk about how acidic or basic a solution is

• pH tells us the quantity of Hydrogen ions in each litre of solution.

• The scale goes from 0 (extremely acidic) to 14 (extremely basic/alkaline), with pure water being a neutral 7.

• The pH scale is logarithmic, meaning that every movement of one number on the scale means a 10-fold change in the number of H⁺ ions

ACIDS AND BASES IN THE LAB

Strong acids react noticeably with many metals and with the chemicals that make up living tissue.  This makes acid hazardous in the lab

• When acids and bases react together, they neutralize one another. If the proper amounts of acid and base are mixed, the result is water and a salt

Some chemicals can act as an acid to neutralze a base AND as a base to neutralize an acid. Sodium hydrogencarbonate, NaHCO_3(s) (baking soda) is an example. Because of this, it is often a key part of safety supplies in chemical laboratories. 

2.4 WATER IS WERID

• The only substance that exists on Earth in large quantities in all three states?

• Less dense in its solid state (ice) than its liquid state so it floats on top of lakes 

         in the winter instead of sinking

WATER IS WEIRD BECAUSE ITS MOLECULES ARE WEIRD

They’re BENT
They’re POLAR

• The oxygen and hydrogen atoms share 2 electrons in each O-H bond.

• But the O atom  attracts the electrons more strongly than the H atoms, because it has more protons

• So the electrons spend more time around the oxygen atom, giving it a slightly negative charge, and the hydrogen a slightly positive charge. 

WATER IS A POLAR MOLECULE

• Because of the unequal electron distribution, water molecules have a positive pole (the hydrogen end) and a negative pole (the oxygen end) = DIPOLE
  

WATER MOLECULES ARE ATTRACTED TO EACH OTHER

• (+) end is attracted to (-) end and a hydrogen bond is formed.
  

  INTERMOLECULAR AND INTRAMOLECULAR FORCES     

  • Intermolecular forces are

      between molecules

      (i.e. hydrogen bonds.

  • Intramolecular forces

      are within molecules 

      (i.e. covalent bonds).
  

  Although hydrogen bonds are much weaker than covalent bonds, they are  the strongest intermolecular bond.

  HYDROGEN BONDS AND ITS POLARITY  EXPLAIN A LOT OF WATER’S WEIRD PROPERTIES

  • High boiling and melting point:  lots of energy is needed to break the hydrogen bonds between water molecules to melt ice or to boil and evaporate water (evaporative cooling)
    
    

ICE IS LESS DENSE THAN WATER

Water expands when it freezes because the polar molecules arrange themselves in an open pattern held together by hydrogen bonds

HIGH SURFACE TENSION

Water has high surface tension because the hydrogen bonds pull the molecules together into the smallest possible area

THE LARGE FORCES OF ATTRACTION (H BONDS) BETWEEN POLAR WATER MOLECULES AND THE SIDES OF CONTAINERS CAUSES:

concave meniscus, capillary action

CAPILLARY ACTION IS THE FORCE THAT DRAWS WATER UP FROM ROOTS TO THE LEAVES OF TALL TREES

Capillary action is defined as the spontaneous flow of a liquid into a narrow tube or porous material. This movement does not require the force of gravity to occur.