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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