Elements and Compounds Chapter 3 Hein and Arena Eugene Passer Chemistry Department Bronx Community College © John Wiley and Sons, Inc Version 2.0 12th Edition

Chapter Outline 3.1 Elements 3.6 Elements in Their Natural States 3.2 Distribution of Elements 3.7 Elements that Exist as Diatomic Molecules 3.3 Names of the Elements 3.4 Symbols of the Elements 3.8 Compounds 3.5 Introduction to the Periodic Table 3.9 Chemical Formulas

3.1 Elements

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

Each element has a number. All known substances on Earth and probably the universe are formed by combinations of more than 100 elements. Each element has a number. Beginning with hydrogen as 1, the elements are numbered in order of increasing complexity.

Most substances can be decomposed into two or more simpler substances. Water can be decomposed into hydrogen and oxygen. Table salt can be decomposed into sodium and chlorine. An element cannot be decomposed into a simpler substance.

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

3.2 Distribution of Elements

Elements are not distributed equally by nature. Oxygen is the most abundant element in the human body (65%). Oxygen is the most abundant element in the crust of the earth (49.2%). In the universe, the most abundant element is hydrogen (91%) and the second most abundant element is helium (8.75%).

Distribution of the common elements in nature. 3.2

3.3 Names of the Elements

Sources of Element Names Greek-Color Iodine: from the Greek iodes meaning violet. Latin- Property Fluorine: from the Latin fluere meaning to flow. The fluorine containing ore fluorospar is low melting. German- Color Bismuth: from the German weisse mass which means white mass. Location Germanium: discovered in 1866 by a German chemist. Famous- Scientists Einsteinium: named for Albert Einstein.

3.4 Symbols of the Elements

A symbol stands for the element itself one atom of the element a particular quantity of the element

Rules governing symbols of the elements are: Symbols have either one or two letters. If one letter is used it is capitalized. C carbon H hydrogen If two letters are used, only the first is capitalized. Ba barium Ne neon

These symbols have carried over from the earlier names of the elements (usually Latin). A number of symbols appear to have no connection with the element. Most symbols start with the same letter as the element.

Metals, Nonmetals and Metalloids

Metals

Most elements are metals Metals are solid at room temperature. Mercury is an exception. At room temperature it is a liquid. Metals are good conductors of heat and electricity. Most elements are metals physical properties of metals Metals are malleable (they can be rolled or hammered into sheets). Metals have high luster (they are shiny).

Most elements are metals Metals have high densities Metals are ductile (they can be drawn into wires). Most metals have a high melting point. Most elements are metals Metals have high densities

Examples of Metals gold lead iron

Chemical Properties of Metals 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 sulfur. chlorine. oxygen. In nature, minerals are formed by combinations of the more reactive metals with other elements.

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.

Nonmetals

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.

Physical State at Room Temperature phosphorous carbon Solid sulfur selenium iodine

Physical State at Room Temperature liquid bromine

gas nitrogen, oxygen fluorine, chlorine Physical State at Room Temperature gas nitrogen, oxygen fluorine, chlorine helium, neon, argon, krypton, xenon, radon

Metalloids

Metalloids have properties that are intermediate between metals and nonmetals

The Metalloids boron silicon germanium arsenic antimony tellurium polonium

Metals are found to the left of the metalloids Nonmetals are found to the right of the metalloids.

3.5 Introduction to the Periodic Table

N 7 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. N 7

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 These elements are known as the noble gases. They are nonreactive. Ar Kr Xe Rn

3.6 Elements in Their Natural States

Most substances around us are mixtures or compounds. THE NOBLE METALS Gold Au Silver Ag Platinum Pt Some elements are found in pure form.

Most substances around us are mixtures or compounds. THE NOBLE GASES Helium He Neon Ne Argon Ar Krypton Kr Xenon Xe Radon Rn Some elements are found in pure form.

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 N2 and O2.

3.7 Elements That Exist as Diatomic Molecules

A diatomic molecule contains exactly two atoms of the same or different elements.

Occurrence of Diatomic Molecules Hydrogen H Not found in nature. H2 Found in nature. Nitrogen N N2

Hydrogen gas is found in volcanoes and it can be prepared in the laboratory. In both cases it is diatomic hydrogen, H2. Air is about 21% oxygen by volume. Oxygen can also be prepared in the laboratory. In both cases it is diatomic oxygen, O2.

Water has the formula H2O. It does not contain free hydrogen, H2 or free oxygen, O2. The H2 part of H2O means that 2 atoms of hydrogen are combined with one atom of oxygen in the water molecule. H2 O2 H2O

3.8 Compounds

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.

Molecules

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. 3.5

Ionic Compounds

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. 3.5

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.

Ionic Compound Formulas

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 NaCl does not mean that a molecule of NaCl exists. The formula NaCl 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 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. 3.3

3.9 Chemical Formulas

calcium CaCl2 chloride chemical formulas Serve as abbreviations of the names of compounds. CaCl2 calcium chloride

calcium CaCl2 chlorine chemical formulas Tell which elements the compound is composed of and how many atoms of each element are present in a formula unit. CaCl2 calcium chlorine

Ca calcium CaCl2 Cl chlorine chemical formulas Show the symbols of the atoms of the elements present in a compound. CaCl2 Ca calcium Cl chlorine

CaCl2 chemical formulas Show the ratio of the atoms of the elements present in a compound. CaCl2

Rules for Writing Chemical Formulas

When a formula contains one atom of an element, the symbol of that element represents the one atom. The number one (1) is not used as a subscript.

NaCl indicates the element sodium (one atom) indicates the element chlorine (one atom)

When the formula contains more than one atom of an element, the number of atoms is indicated by a subscript written to the right of the symbol of that atom.

H3PO4 indicates the element oxygen (O) indicates indicates the element hydrogen (H) indicates the element phosphorous (P) indicates 4 O atoms indicates 3 H atoms

When the formula contains more than one of a group of atoms that occurs as a unit, parentheses are placed around the group, and the number of units of the group is indicated by a subscript placed to the right of the parentheses.

Ba3(PO4)2 indicates the element barium indicates three Ba atoms indicates the phosphate group composed of one phosphorous atom and four oxygen atoms indicates three Ba atoms

Formulas written as H2O, H2SO4, Ca(NO3)2 and C12H22O11 show only the number and kind of each atom contained in the compound; they do not show the arrangements of the atoms in the compound or how they are chemically bonded to each other.

H2O

The End