Diversity of Matter
When naming binary ionic compounds, follow the following steps
Examples
1. NaCl
2. Fe2O3
By now. you should be able to understand how the following names are derived:
When naming ionic compounds with polyatomic ions, the same rules as naming binary ionic compounds.
Examples:
1. CuSO4
By now. you should be able to understand how the following names are derived:
The simplest ratio formula is also referred to as the empirical formula. All ionic formulas are empirical formulas.
Molecular compounds are formed by the covalent bonding between two non metals. The elements share electrons.
Prefixes are used and enable the student to know how many atoms of each element there is in the covalent compound. The first non-metal keeps its name, and the second non-metal ends in ide
Naming binary molecular compounds is done by adding prefixes and element names, then adding ide in the end.
Examples
Naming acids
The classical naming system has three main rules
The classical naming system for acids is different from the IUPAC system of naming. The table below illutsrates these differences.
| Classical | IUPAC System |
|---|---|
| hydrochloric acid | aqueous hydrogen chloride |
| sulfuric acid | aqueous hydrogen sulfate |
| Nitric acid | aqueous hydrogen nitrate |
Naming bases
The name of the base is the name of the ionic hydroxide. For example:
Which, as you may have noticed, is similar to naming ionic compounds.
Matter is composed of indestructible, indivisible atoms which are identical for one element, but different from other elements.
Element is a species of atom having the same number of protons in its atomic nuclei (that is, the same atomic number. Solid elements, such as sulfur, aluminium, and carbon, are only very slightly soluble in water. Mercury, the only liquid element, is also largely insoluble. The gaseous elements, including oxygen and chlorine, are more soluble.
A compound is a substance formed when two or more chemical elements are chemically bonded together. In mixtures, the substances present are not chemically bonded together. Ionic compounds are made up of ions and are mostly soluble in water although to varying extentes. For example sodium hydroxide and most sulfates are highly soluble in water while Lead(II) chloride and most phosphates, are only slightly soluble.
Classifying matter
John Dalton - 1766 - 1844: Also called the Billiard Ball model. The theory states that matter is composed od indestructible, indivisible atoms, which are identical for one element but different from other elements.
J.J. Thomson - 1856 - 1940: Also called the raisin bun model. States that matter is composed of atoms that contain electrons (negatively charged particles) embedded in a positively charged material. The kind of element is characterized by the number of electrons in the atom.
Ernest Rutherford - 1871 - 1937: Also called the nuclear model. States that an atom is composed of a very tiny nucleus, which contains positive charges and most of the mass of the atom. Very small negative electrons occupy most of the volume of the atom.
Neils Bohr - 1885 - 1962: Also called the Orbital Model. States that electrons travel in the atom in circular orbits with quantized energy, which is restricted to only certain discrete quantities. There is a maximum number of electrons that can be allowed in each orbit. Electrons can jump to a higher energy level when a photon is absorbed. On the other hand, a photon is emitted when the electron drops to a lower energy level.
These theories have established the concepts of the atom. An atom is, therefore, composed of protons, neutrons, and electrons. Atoms of the same element have the same number of protons and electrons but may have a varying number of neutrons.
The mass number of an atom is equal to the number of particles in the nucleus (protons and neutrons). The atomic number of an atom is equal to the number of protons in the nucleus.
In the case of Carbon, as shown below, the mass number is 14, and the atomic number is 6.
Isotopes are variants of a particular chemical element have the same number of protons but different numbers of neutrons in each atom. Any sample of an element found in nature is a mixture of different isotopes. Each isotope will occur in different proportions, usually given as a percentage.
An illustration of mass number, atomic number and carbon isotopes.
The periodic table (aka the periodic table of elements) is a table arrangement of the chemical elements arranged by atomic number, electron configuration, and chemical properties. The organization of the periodic table can be used to derive relationships between the various element properties, and to predict chemical properties and behaviours of undiscovered or newly synthesized elements. The first periodic table was developed by the Russian Chemist Dmitri Mendeleev in 1869, to illustrate periodic trends of the then-known elements. The modern periodic table now provides a useful framework for analyzing chemical reactions, and continues to be widely used in chemistry, nuclear physics and other sciences. Some discussion remains ongoing regarding the placement and categorisation of some elements, the future extension and limits of the table, and whether there is an optimal form of the table. Various other tables and iterations have been published by several scientists but the standard table format is still the go-to format.
Mendeleev's periodic table in 1885. (Source: Wikipedia-CC BY-SA 3.0)
Other less popular types of display of chemical elements. Theodor Benfey's spiral periodic table. (Source: Wikipedia-CC BY-SA 3.0)
A group or family is a vertical column in the periodic table. Groups usually have more significant periodic trends than periods and blocks, explained below. Modern quantum mechanical theories of atomic structure explain group trends by proposing that elements within the same group generally have the same electron configurations in their valence shell
The groups are numbered numerically from 1 to 18 from the leftmost column (the alkali metals) to the rightmost column (the noble gases). Elements in the same group tend to show patterns in atomic radius, ionization energy, and electronegativity. From top to bottom in a group, the atomic radii of the elements increase. Since there are more filled energy levels, valence electrons are found farther from the nucleus. From the top, each successive element has a lower ionization energy because it is easier to remove an electron since the atoms are less tightly bound. Similarly, a group has a top-to-bottom decrease in electronegativity due to an increasing distance between valence electrons and the nucleus.
A period is a horizontal row in the periodic table. Elements in the same period show trends in atomic radius, ionization energy, electron affinity, and electronegativity. Moving left to right across a period, atomic radius usually decreases. This occurs because each successive element has an added proton and electron, which causes the electron to be drawn closer to the nucleus.
Specific regions of the periodic table can be referred to as blocks in recognition of the sequence in which the electron shells of the elements are filled.
A detailed periodic table of elements (Source: Wikipedia-CC BY-SA 3.0)
A compound is a formed when two or more elements combine together in a chemical reaction.
Compounds can be classified as acids, bases or neutral compounds. Acids turn blue litmus paper red, bases turn red litmus paper blue, and neutral compounds cause no effect on litmus papers.
Compounds can also be classified depending on the type of bond joining the component elements, such as ionic bond (Ionic compounds) or covalent bond (Molecular compounds).
Ionic compounds are created by the reaction between a metal and a non-metal. Ionic compounds are solids in nature and soluble in water. They conduct electricity in aqueous solution.
Ionic hydrates are ionic compounds that contain loosely bonded water molecules. Hydrated compounds appear different from unhydrated compounds. For example, hydrated copper II sulfate forms blue crystals, while the unhydrated form is a white powder.
Molecular compounds are created by the reaction between a non-metal and a non-metal. Molecular compounds are either solid, liquid or gases, depending on the component elements. Their solubility also varies, and they do not conduct electricity in aqueous solutions.
A molecule is a group of nonmetal atoms held together by covalent bonds. The molecular formula indicates the number of atoms of each type.
A chemical reaction is said to have occurred when one of the following observations are made. These observations can be classified into physical, chemical or nuclear changes.
State or energy change: This involves the change from solid to liquid or to gaseous state. The energy change is usually small. There is no new substance formed.
This may include color change, change in odor, physical state and energy change. A new substance is formed, and the changes may be irreversible. Chemical changes are associated with moderate energy changes, higher than physical changes.
Nuclear changes often result in emission of radiation energy. New elements are formed, and the energy change is usually much larger than chemical changes.
The evidence of a chemical reaction can be explained using the major aspects that change when a chemical reaction occurs. These include:
a. Color change: A color change could indicate that the product is different from the reactants. For example if a solution changes from colorless to blue.
b. Odor change: The final products may have a different smell from the reactants.
c. State change: If the products are of a different state compared to the reactants. Mostly, for example, if a substance changes into a gas or if a solid precipitate is formed.
d. Energy change: When a chemical reaction occurs, energy, in form of heat, light, sound, or electricity is either absorbed by the reaction or emitted from the reaction. Combustion of fuels is obviously a good example. If energy is absorbed by the reaction, the reaction is called endothermic , if energy is released by the reaction, the reaction is called exothermic.
A chemical reaction can be explained using the kinetic molecular theory. In this theory, it is believed that the smallest entities of a substance are in continuous motion. These entities may be atoms, ions, or molecules. As they move about, the entities collide with each other and with objects in their path. If certain entities collide with sufficient energy, the components of the entities will rearrange to form new entities. The collisions between entities may result in sharing or losing electrons as the entities attempt to achieve a more stable electron arrangement, resulting in a chemical reaction. This is known as collision-reaction theory.
Reactions can be classified into five different types as follows:
Solubility denotes the interaction between two substances, where one is a solvent (the liquid component). The other part is usually a solid (the solute) but in many cases, it can also be gas (such as carbonated drinks) or another liquid. Depending on the degree of solubility, the combination will be called a solution (if readily soluble), a suspension and precipitate.
The appearance of mixtures under varying levels of solubility. (Source: Wikipedia-CC BY-SA 3.0)
Ionic compounds have varying levels of solubility in water from those that dissolve readily, to those that don't. Compounds that dissolve easily form solutions, while those that do not dissolve easily form precipitates. A precipitate shows solid undissolved material at the bottom of the tube, and the liquid cloudy part is called supernatant. When a solute’s concentration is equal to its solubility, the solution is said to be saturated with that solute. If the solute’s concentration is less than its solubility, the solution is said to be unsaturated. A solution that contains a low concentration of solute is called dilute, and one with a relatively high concentration is called concentrated. When a saturated solution is allowed to evaporate, crystals might form in a process called crystallization.
| Ion | Solubility | Exceptions |
|---|---|---|
| NO3– | soluble | No exceptions |
| ClO4– | soluble | No exceptions |
| Cl– | soluble | except Ag+, Hg22+, Pb2+ |
| I– | soluble | except Ag+, Hg22+, Pb2+ |
| SO42- | soluble | except Ag+, Hg22+, Pb2+, Ca2+, Ba2+, Sr2+. |
| CO32- | Insoluble | except Group IA and NH4+ |
| PO43- | Insoluble | except Group IA and NH4+ |
| OH- | Insoluble | except Group IA, Ca2+, Ba2+, Sr2+ |
| S2- | Insoluble | except Group IA, IIA and NH4+ |
| Na+ | soluble | No exceptions |
| K+ | soluble | No exceptions |
| NH4+ | soluble | No exceptions |
Some liquids mix (dissolve) and are said to be miscible. Polar liquids are soluble in other polar liquids. For example, ethanol, sulfuric acid, and ethylene glycol (antifreeze) are examples of polar liquids that are completely miscible with water. Non-polar liquids dissolve in other non-polar liquids. For example, motor oil is miscible with gasoline. Liquids that do not mix are called immiscible and usually form separate layers. Two liquids, such as bromine and water, that are of moderate solubility are defined as partially miscible. In the case of the bromine and water, the mixture forms two interacting layers, the upper layer is water, saturated with bromine, and the lower layer is bromine saturated with water.
A chemical bond results from the simultaneous attraction of electrons by two nuclei, the first nucleus is for the same atom, and the second nucleus is for the atom of the other element.
Electrons are located at certain specific energy levels around the nucleus called orbitals. An orbital is a region of space where there is a high probability of finding electrons of a particular energy. The number of energy levels occupied by electrons around an atom corresponds with the 'period' number on the periodic table. Each energy level has a maximum number of electrons that it can accommodate. Since electrons are pulled towards the nucleus, the strength of the attraction reduces as the number of energy levels increases. The electrons that occupy the outermost energy level are called valence electrons. Being positioned the farthest from the nucleus, they experience the lowest attraction force.
An orbital can be occupied by either one or two electrons. When occupied by one electron, these are called Bonding electrons . When occupied by two electrons, these are called Lone pairs. The maximum number of bonding electrons determines an atom’s bonding capacity, which is the maximum number of single covalent bonds formed by an atom.
Each energy level has a maximum number of electrons. Because electrons repel each other, they tend to spread out in the orbitals as far from each other as possible. There are 4 planes that allow electrons to be farthest from each other; you can think of these as North, South, East and West of the nucleus; electrons will spread out to these positions until each has a bonding electron before electrons start forming lone pairs.
Maximum numbers of electrons per orbital and examples of electron configurations, showing valence electrons. Lewis dot diagrams for 6 elements in the periodic table.
Electronegativity is the tendency for an atom to attract electrons to itself when it is chemically combined with another element. Assuming the basic principle that the further away the electron is to the nucleus, the less the attraction, means the electronegativity will reduce as the energy levels increase. So electronegativity decreases as you go down the group as the periods increase. As the number of electrons on the outermost shell increases, there is also increased attraction to the nucleus, so electronegativity increases as the groups increase, even within the same period. In general, metals tend to have low electronegativity and non-metals tend to have high electronegativity. Electronegativity (actually referring to the difference between the electronegativity of the two bonding elements) influences the type of bonding that can occur between two or more elements and influences the polarity of a bond.
Trends in electronegativity of elements in the periodic table.
Polar molecules have one end that is slightly negative and one end that is slightly positive. Bond polarity depends on the electronegativity of the bonded atoms. Covalent bonds are polar if the atoms of the two elements have different electronegativity. The higher the electronegativity difference, the higher the polarity. Electrons spend more time around the nucleus with the higher electronegativity making that side more negative than the opposite side.
A bond dipole (or dipole moment) is the charge separation that occurs as a result of the different electronegativity of the bonded atoms. It is represented by an arrow that points from lower to higher electronegativity.
Polar bonds may result in non-polar molecules when the bond dipoles cancel out leaving a molecular dipole of zero. The carbon dioxide molecule is an great example for such.
Molecules that are symmetrical are non-polar because the dipole moments balance. The methane molecule can be used to illustrate this as shown in the figure below. Water, on the other hand, is asymmetrical, with the oxygen atom on one side and the two hydrogen atoms on the other side, resulting in a polar molecule. See figure below.
Illustration of bond dipoles and polar and non-polar bonds.
Empirical formula: shows the simplest whole number ratios of atoms in the compound, for example, CH2O. These are rarely used in chemistry.
Molecular formula: shows the actual number of atoms that are covalently bonded to make each molecule. For example C2H4O2.
Lewis dot formula: shows the electrons sharing in covalent bonds and the formation of stable electron octets.
Structural formula: Is also called structural diagram. It shows which atoms are bonded and the type of covalent bond. It is possible to use structural formulas to show isomers.
Stereochemical formula: This is an advanced structural formula drawn in a way to show the 3D structure, it represents bond angles and whether an atom is above or below the surface of the paper.
VSEPR stands for Valence – Shell – Electron – Pair – Repulsion. Valence electrons repel each other electrostatically and position themselves so that they maximize the distance between them. The molecular shape is determined by the positions of the electron pairs when they are a maximum distance apart. Only the valence electrons of the central atom(s) are important for molecular shape. Bonded pairs of electrons and lone pairs of electrons are treated approximately equally.
Determining Molecular Shape
Illustration of bond angles showing electrons repelling one another.
From top left: Linear, Trigonal planar, Tetrahedral, Trigonal Pyramidal and Bent models. (Source: Wikipedia-CC BY-SA 3.0)