CH 1000 MOD 1 REVIEW HW

CH1000 Fundament als of Chemistry Module 1 – Chapter 3

Elements and Atoms

• What is an element? • An element is a fundamental substance that cannot be broken down by chemical

means into a simpler substance.

• Elements are the building blocks of matter. • Elements can occur naturally or be synthesized in labs.

• The smallest unit of an element that retains its properties and chemical behavior is called an atom. • Atoms are made up of subatomic particles, but they do not have the properties of the

element

Elements

•Ten elements make up almost 99 % of the mass of the Earth’s crust, seawater and atmosphere.

•Oxygen accounts for about 20 % of the atmosphere and is found in nearly all rocks, sand and soil.

Symbols of the Elements •Each element has an abbreviation called a symbol.

•The first letter of a symbol must always be capitalized.

•If a second letter is needed, it should be lowercase.

Introduction to the Periodic Table

•Elements with similar chemical properties are placed in columns called groups.

•Four groups have special identifying names, like Noble Gases, in group 8A, which are all unreactive gases.

Introduction to the Periodic

Table

•The eight tall columns are called representative elements, or main group elements. These are shown in red.

•The elements in the center are called the transition metals, or sometimes the “inner transition metals.” These are shown in purple.

Introduction to the Periodic Table

•Elements can be further classified as metals, metalloids and nonmetals.

•Notice the bold, black “staircase” on the table. Everything to the left of the staircase is a metal and everything to the right of the staircase is a non metal.

• The exception is Hydrogen, which is why some periodic tables will show hydrogen disconnected from the main body of the table.

•The elements in grey touching the “staircase” are called metalloids, or semiconductor metals. These metals are used in the semiconductor industry.

Metals, Nonmetal s and Metalloids

• Solid at room temperature (except mercury) • Shiny • Good conductors of heat and electricity • Malleable (can be shaped) • Ductile (can be drawn into wires) • Most metals have a high melting point and density

Metals

• Not shiny • Have fairly low melting points and densities • Are poor conductors of heat and electricity

Non Metals

• Metalloids have properties between metals and nonmetals.

• These elements are positioned diagonally on the Periodic Table separating the metals and nonmetals.

Metalloid s

Diatomic Elements

•Diatomic molecules contain exactly two atoms

•Seven elements exist as diatomic molecules and are shown in the table to the left

•Diatomic elements can be separated.

Compounds

•A compound is a substance containing two or more elements that are chemically combined in a definite proportion by mass

•Compounds, unlike elements, can be decomposed chemically into simpler substances

•Elements in compounds are always combined in whole number ratios.

Molecular and Ionic Compounds

•Compounds fall into two general types, molecular and ionic.

•Molecular compounds are held together by covalent bonds

•Ionic compounds are held together by attractive forces between the positive and negative charges.

Molecules and Ions

• What is a molecule? • Molecules are the smallest unchanged individual unit of a compound formed by two or

more atoms.

• A molecule cannot be further divided without destroying its identity.

• What is an ion? • Ions are charged atoms or groups of atoms. Ions can be positively or negatively

charged.

• A positively charged ion is called a cation. • A negatively charged ion is called an anion.

Writing Formulas of Compound s

The formula of a compound contains the symbols of all the elements in the compound

When a formula contains only one atom of an element, the number 1 is not needed as a subscript

When a formula contains more than one atom of an element, the number is indicated by a subscript written after the symbol

Writing Formulas of Compound s

When the formula contains more than one of a group of atoms that occur as a unit, parentheses are placed around the group and the number of units is represented by a subscript outside the parentheses.

Formulas show the number and kind of atoms in a compound, but not the connectivity of the elements.

Composition of Compounds

•A particular compound always contains the same elements in the same proportions by mass no matter what the origin.

•The Law of Definite Composition states that a compound always contains two or more elements chemically combined in a definite proportion by mass.

Composition of Compounds

•The Law of Multiple Proportions states that atoms of two or more elements may combine in different ratios to produce more than one compound.

Reading Review

What is the name of the periodic table group 8A?

What is the molecular formula for the diatomic molecule, nitrogen?

What is the difference between a cation and anion?

What is the atomic number and symbol for the potassium?

What are the elements in the center section of the periodic table called?