Elements, Atoms, and Ions Chapter 4 Elements, Atoms, and Ions
Elements Elements cannot be broken down by ordinary chemical change to simpler forms of matter. Metals, nonmetals, metalloids (semimetals) Each element is assigned a unique chemical symbol.
TYPES OF ELEMENTS METALS -- shiny, conduct heat and electricity, ductile (can be pulled into wires), malleable (can be rolled into sheets) NONMETALS -- dull, brittle, poor conductors METALLOIDS -- have properties of both metals and nonmetals POSITION ON PERIODIC CHART
Copyright © Cengage Learning. All rights reserved Each element has a unique one- or two-letter symbol. First letter is always capitalized and the second is not. The symbol usually consists of the first one or two letters of the element’s name. Examples: Oxygen O Krypton Kr Sometimes the symbol is taken from the element’s original Latin or Greek name. Examples: Gold Au aurum Lead Pb plumbum Copyright © Cengage Learning. All rights reserved
ELEMENTS FROM LATIN Iron -- Fe -- ferrum Lead -- Pb -- plumbum Copper - Cu - cuprum Mercury-Hg- hydrargyrum Gold -- Au -- aurum Silver-Ag- argentum Antimony-Sb-stibium Sodium -Na-natrium Potassium -K- kalium tin- Sn - stannum
The Atom From the Greek, atomos meaning “not cut” Law of Conservation of Mass: No detectable gain or loss of mass occurs in chemical reactions. Mass is conserved. Law of Definite Proportions: In a given chemical compound, the elements are always combined in the same proportions by mass. Water always contains 8 g of oxygen for every 1 g of hydrogen. Carbon dioxide always contains 2.7 g of oxygen for every 1 g of carbon.
Dalton’s Atomic Theory Matter consists of tiny particles called atoms. Atoms are indestructible. In chemical reactions, the atoms rearrange but they do not themselves break apart. In any sample of a pure element, all the atoms are identical in mass and other properties. The atoms of different elements differ in mass and other properties. In a given compound the constituents atoms are always present in the same fixed numerical ratio.
Copyright © Cengage Learning. All rights reserved J. J. Thomson (1898—1903) Postulated the existence of electrons using cathode-ray tubes. The atom must also contain positive particles that balance exactly the negative charge carried by particles that we now call electrons. Copyright © Cengage Learning. All rights reserved
Copyright © Cengage Learning. All rights reserved Cathode-Ray Tube Copyright © Cengage Learning. All rights reserved
William Thomson (Plum Pudding Model) Reasoned that the atom might be thought of as a uniform “pudding” of positive charge with enough negative electrons scattered within to counterbalance that positive charge. Copyright © Cengage Learning. All rights reserved
Copyright © Cengage Learning. All rights reserved Ernest Rutherford (1911) Explained the nuclear atom. Atom has a dense center of positive charge called the nucleus. Electrons travel around the nucleus at a relatively large distance. A proton has the same magnitude of charge as the electron, but its charge is positive. Copyright © Cengage Learning. All rights reserved
Rutherford and Chadwick (1932) Most nuclei also contain a neutral particle called the neutron. A neutron is slightly more massive than a proton but has no charge. Copyright © Cengage Learning. All rights reserved
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Millikan’s Oil Drop Experiment
Copyright © Cengage Learning. All rights reserved The atom contains: Electrons – found outside the nucleus; negatively charged Protons – found in the nucleus; positive charge equal in magnitude to the electron’s negative charge Neutrons – found in the nucleus; no charge; virtually same mass as a proton Copyright © Cengage Learning. All rights reserved
Copyright © Cengage Learning. All rights reserved The nucleus is: Small compared with the overall size of the atom. Extremely dense; accounts for almost all of the atom’s mass. Copyright © Cengage Learning. All rights reserved
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Why do different atoms have different chemical properties? The chemistry of an atom arises from its electrons. Electrons are the parts of atoms that “intermingle” when atoms combine to form molecules. It is the number of electrons that really determines chemical behavior. Copyright © Cengage Learning. All rights reserved
ATOMIC THEORY Atomic number = # of protons. In a neutral atom the number of protons equals the number of electrons. Mass number = number of protons plus the number of neutrons. Mass number minus the atomic number equals the number of neutrons.
Atomic mass -- mass of an element relative to the carbon 12 isotope Atomic mass -- mass of an element relative to the carbon 12 isotope. C --12 is assigned a mass of 12 atomic mass units and the masses of other elements are determined relative to it. Atomic mass unit (amu) = 1/12 the mass of the C -- 12 isotope.
Isotopes -- atoms having the same number of protons but a different number of neutrons. Ions -- atoms that have acquired a charge by gaining or losing electrons. Metals usually lose electrons and nonmetals usually gain electrons. Metallic ions normally have a + charge and nonmetallic ions a negative charge. Cation (+ ion) and anion(- ion)
Copyright © Cengage Learning. All rights reserved Two Isotopes of Sodium Copyright © Cengage Learning. All rights reserved
Copyright © Cengage Learning. All rights reserved Isotopes X = the symbol of the element Z = the atomic number (# of protons) A = the mass number (# of protons and neutrons) Copyright © Cengage Learning. All rights reserved
Copyright © Cengage Learning. All rights reserved The Periodic Table The periodic table shows all of the known elements in order of increasing atomic number. Copyright © Cengage Learning. All rights reserved
PERIODIC TABLE 1. History Döbereiner -- Law of Triads Newlands -- Law of Octaves Meyer -- worked with physical properties of elements Mendeleev -- worked with chem properties and arranged according to atomic mass.
Moseley -- arranged elements according to increasing atomic number Moseley -- arranged elements according to increasing atomic number. This is how the periodic chart is arranged today. 2. Vertical columns -- families -- similar chem and physical properties. 3. Horizontal rows -- periods or series -- go from metallic to nonmetallic properties. 4. Central section -- transition elements 5. Bottom, separated two rows -- rare earth, inner transition elements; lanthanide & actinide series.
Copyright © Cengage Learning. All rights reserved The Periodic Table The periodic table shows all of the known elements in order of increasing atomic number. Copyright © Cengage Learning. All rights reserved
Copyright © Cengage Learning. All rights reserved The Periodic Table Most elements are metals and occur on the left side. The nonmetals appear on the right side. Metalloids are elements that have some metallic and some nonmetallic properties. Copyright © Cengage Learning. All rights reserved
Physical Properties of Metals Efficient conduction of heat and electricity Malleability (they can be hammered into thin sheets) Ductility (they can be pulled into wires) A lustrous (shiny) appearance Copyright © Cengage Learning. All rights reserved