ELEMENTS AND THE PERIODIC TABLE



Matter and Atomic Structure

CLASSIFICATON OF MATTER

• Matter – anything that has mass and occupies space.

o Pure Substance – All the particles that make up the substance are the same; the substance has constant properties.

▪ Elements

• Can not be broken down into different types of atoms; they only contain one type of atom (ex. iron, mercury).

• Represented by a chemical symbol (ex. Fe, Hg).

▪ Compounds

• Contain two or more different elements (different types of atoms) bonded together in a fixed proportion.

• Identified by chemical formulas (ex. CO2, H2O).

o Mixtures – contain two or more pure substances that can be separated by physical means.

▪ Homogeneous Mixtures

• Have only one visible component (ex. coffee, brass).

• Also called solutions.

▪ Heterogeneous Mixtures

• Contain two or more visible components. (ex. pizza)

• Also referred to as mechanical mixtures; they can generally be separated more easily than solutions by, for example, filtration, evaporation of the solvent, and by using one’s hands to remove individual components.

PROPERTIES OF MATTER

• A physical property is a characteristic of a substance (ex. state, color, odor, lustre, texture, hardness, crystal form, mass, volume, density, solubility, viscosity, malleability, ductility, melting point, boiling point).

o A physical change is a change in the size or form of a substance, and it does not change the chemical properties of the substance.

• A chemical property is a characteristic behavior that occurs when a substance changes to a new substance (ex. reacts with acid, reacts with water, combustible).

o The change itself is called a chemical change. A substance is changed into one or more new substances (ex. burning, cooking, rusting).

CHEMICAL REACTIONS

• There are clues that a chemical change has occurred:

o A new color appears.

o Heat or light is given off.

o Bubbles of gas form.

o A precipitate forms in a liquid.

o The change is difficult to reverse.

• Chemical reactions have a standard format when written:

o Reactants Products

A + B ( C + D

• Chemical reactions can be used to make new substances and are also useful for identifying unknown substances (ex. testing for different gases).

THE PERIODIC TABLE OF ELEMENTS

• Helps to explain and predict both chemical and physical properties of different elements.

• It is a means of organizing all of the elements.

o Metals are toward the left side of the table and are located below the staircase.

▪ Tend to be shiny and malleable solids that are conductors of heat and electricity.

o Nonmetals are toward the right side of the table, above the staircase.

▪ Tend to be dull and brittle. There are found to be solids, liquids, and gases, all of which are insulators.

o There metals and nonmetals located directly above and below the staircase that exhibit metallic and nonmetallic properties. These elements are also often referred to as metalloids.

• Elements that are within the same column of the periodic table are called chemical families or groups.

o There are four key families and each tend to have the same physical and chemical properties.

▪ Alkali metals – Group 1

▪ Alkaline Earth metals – Group 2

▪ Halogens – Group 17

▪ Noble Gases – Group 18

o Hydrogen is unique because it exhibits properties of both metals and nonmetals. It is located above group one because it has one valence electron just like the alkali metals.

• Rows of the periodic table are called chemical periods.

o They are numbered 1 to 7.

o The lanthanides and actinides are classified as metals; they are periods 6 and 7 below the table.

REPRESENTATION OF ATOMIC STRUCTURE

• The Bohr-Rutherford Model of the atom

o Shows that atoms are composed of three subatomic particles:

▪ Protons are heavy and positively charged.

▪ Neutrons have approximately the same mass as protons, but they are neutral.

▪ Electrons have almost no mass and they are negatively charged.

▪ Protons and neutrons are located at the dense core of the atom (the nucleus).

▪ Atoms are electrically neutral because they have the same number of protons and electrons.

o The atomic number of an element indicates the number of protons it has in one atom.

o The atomic weight of an atom indicates the sum of protons and neutrons.

▪ It is measured in atomic mass units (amu).

o The model represents the arrangement of electrons. Electrons orbit the nucleus at different energy levels (aka orbits or shells)

▪ The first shell can only hold up to two electrons, but the second, third and fourth shells can hold up to eight electrons each.

▪ The farther away an electron is from its nucleus, the greater its energy and its tendency to be involved in chemical reactions.

▪ Electrons in the outer-most shell (valence shell) are called valence electrons; they are involved in bonding.

o This theory only applies to elements up to 20 electrons.

• Standard Atomic Notation

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Atomic Mass

Atomic Number

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