Elements and Compounds Outline Elements Distribution of the

Elements and Compounds

Outline Elements Distribution of the elements Names of the elements Symbols of the elements Introduction to the periodic table Elements in their natural states Diatomic molecules Compounds Chemical Formulas

Element An element is a fundamental or elementary substance that cannot be broken down into simpler substances by chemical means.

All known substances are formed from various combinations of just over 100 elements.

Atom The smallest particle of an element that can exist. The smallest unit of an element that can enter into a chemical reaction.

Element names come from Greek, Latin, German, locations, and famous scientists Examples: Iodine: from the Greek iodes meaning violet. Fluorine: from the Latin fluere meaning to flow. Bismuth: from the German weisse mass which means white mass. Germanium: discovered in 1866 by a German chemist. Einsteinium: named for Albert Einstein.

Physical Properties of Metals Most elements are metals. Most metals are solid at room temperature. Metals are good conductors of heat and electricity. Metals are malleable (they can be rolled or hammered into sheets). Metals have high luster (they are shiny). Metals are ductile (they can be drawn into wires). Most metals have a high melting point. Metals have high densities.

Chemical Properties of Metals have little tendency to combine with each other to form compounds. Many metals readily combine with nonmetals to form ionic compounds. They can combine with halogens, sulfur, oxygen … In nature, minerals are formed by combinations of the more reactive metals with other elements.

More Chemical Properties of Metals A few of the less reactive metals such as copper, silver and gold are found in the free state. Metals can mix with each other to form alloys. Brass is a mixture of copper and zinc. Bronze is a mixture of copper and tin. Steel is a mixture of carbon and iron.

Physical Properties of Nonmetals Lack luster (they are dull) Have relatively low melting points Have low densities. Poor conductors of heat and electricity At room temperature, carbon, phosphorous, sulfur, selenium, and iodine are solids.

Metalloids have properties that are intermediate between metals and nonmetals

The Metalloids boron silicon germanium arsenic antimony tellurium polonium

The periodic table was designed by Dimitri Mendelev in 1869. In the table each element’s symbol is placed inside of a box. Above the symbol of the element is its atomic number. 7 N

The elements are arranged in order of increasing atomic number. Elements with similar chemical properties are organized in columns called families or groups. He Ne Ar Kr Xe Rn These elements are known as the noble gases. They are nonreactive.

Most substances around us are mixtures or compounds. Some elements are found in pure form such as copper, gold and silver.

Most substances around us are mixtures or compounds. Air is composed mainly of nitrogen and oxygen gases. Nitrogen and oxygen are composed of tiny two atom molecules of N 2 and O 2. These are both examples of diatomic molecules. A diatomic molecule contains exactly two atoms of the same or different elements.

A compound is a distinct substance that contains two or more elements combined in a definite proportion by weight.

Compounds can be decomposed chemically into simpler substances–that is, into simpler compounds or elements. Elements cannot be decomposed into simpler substances. Atoms of the elements that constitute a compound are always present in simple whole number ratios. They are never present as fractional parts.

There are two types of compounds: molecular and ionic.

A molecule is the smallest uncharged individual unit of a compound formed by the union of two or more atoms.

A water molecule consists of two hydrogen atoms and one oxygen atom. If it is subdivided the water molecule will be destroyed and hydrogen and oxygen will be formed.

An ion is a positively or negatively charged atom or group of atoms.

A cation is a positively charged ion. 3. 5

An anion is a negatively charged ion. 3. 5

Ionic compounds are held together by attractive forces between positively and negatively charged ions.

Sodium Chloride Sodium chloride is a colorless crystalline ionic substance. It is 39. 3% sodium and 60. 7% chlorine by mass. The solid does not conduct electricity. Passing an electric current through the molten salt produces solid sodium and gaseous chlorine.

Sodium Chloride The ultimate particles of sodium chloride are positively charged sodium ions and negatively charged chloride ions.

Sodium Chloride The crystalline structure of sodium chloride is held together by the attractive forces between the positive sodium ions and the negative chloride ions

The actual chemical formulas of ionic compounds express the smallest whole number ratio that exists between the cations and the anions. Sodium chloride and other ionic compounds consist of large aggregates of cations and anions. The formula Na. Cl does not mean that a molecule of Na. Cl exists. The formula Na. Cl means that the ratio of sodium to chlorine in a sodium chloride crystal is one to one.

The ratio of Na+ to Cl- is 1: 1

Compounds can be classified as molecular or ionic. Ionic compounds are held together by attractive forces between their positive and negative charges. Molecular compounds are held together by covalent bonds.

Na. Cl Indicates the element sodium (one atom) Indicates the element chlorine (one atom)

indicates the element oxygen (O) H 3 PO 4 indicates the element hydrogen (H) indicates 3 H atoms indicates 4 O atoms indicates the element phosphorous (P)

indicates the element barium Ba 3(PO 4)2 indicates three Ba atoms indicates the phosphate group composed of one phosphorous atom and four oxygen atoms