Elements • Elements are pure substances that cannot be separated into simpler substances by ordinary laboratory processes. • Elements are the building blocks of matter. • There are 113 elements known today. gold carbon aluminum
Symbols of Elements • Every element has a symbol that represents its name. • Symbols consist of 1 or 2 letters. • Only the first letter in a symbol is capitalized.Examples:1-Letter Symbols 2-Letter SymbolsC carbon Co cobalt N nitrogen Ca calcium F fluorine Al aluminum O oxygen Mg magnesium
Symbols from Latin Names • Several symbols are derived from Latin names. • Some examples are shown below:copper, Cu (cuprum) gold, Au (aurum)iron, Fe (ferrum) silver, Ag (argentum)
Elements in the Body • Carbon, oxygen, and hydrogen are the most abundant elements in the human body.
Physical Properties • The physical properties of an element are the characteristics that can be observed without changing the substance.
Periodic Table The periodic table arranges elements according to similar properties.
Groups on the Periodic Table • On the periodic table, each vertical column is called a groupof elements. • A group contains elements with similar chemical and physical properties. • Each group is identified by a group number at the top of the column. • The representative elementshave group numbers of 1A – 8A. The transition elementsuse the letter “B.”
Numbering Groups • One numbering system for groups assigns the letter A to the representative elements and the letter B to the transition elements. • Another system assigns the numbers 1-18 to the columns across the periodic table.
Group Numbers Group numbers
Representative Elements • Several groups of representative elements are classified by name. Group 1A Alkali Metals Group 2A Alkaline Earth Metals Group 7A Halogens Group 8A Noble Gases
Representative Elements • Group 1A, the alkali metals,includes sodium, lithium, and potassium. • Group 7A, the halogens, includes chlorine, bromine, and iodine.
Periods on the Periodic Table • On the periodic table, each horizontal row is called a period. • A period is identified by a number such as 1, 2, 3, or 4. • Periods 2-7 include representative elements and transition elements.
Location of Periods Period 4
Metals, Nonmetals, and Metalloids NONMETALS METALS METALOIDS
Metals and Nonmetals • Metals • Are located to the left of the heavy line. • Are shiny, ductile, and good conductors. • Metalloids • Are elements along the heavy line. • Have properties of both metals and nonmetals. • Nonmetals • Are located to the right of the heavy line. • Are dull, brittle, poor conductors, and good insulators.
Atomic Theory • Matter is composed of tiny particles called atoms. • Atoms in each element are similar and different from atoms of other elements. • Atoms of two or more different elements combine in simple ratios to form compounds. • A chemical reaction involves changes in the arrangements of atoms.
Subatomic Particles • Chemists are interested in three particles in atoms:protons, electrons, and neutrons. • Protons have a positive (+) charge; electrons have a negative (-) charge. • Like charges repel and unlike charges attract.
Rutherford’s Gold-Foil Experiment • Most positive particles aimed at atoms of gold went straight through the atoms. Only a few were deflected. • Rutherford concluded that atoms have a small, dense nucleus with a positive charge.
Structure of the Atom • An atom consists of a nucleus and a cloud of electrons. • The nucleus contains all of the protons and neutrons. • The rest of the atom, which is mostly empty space, is occupied by the electrons.
2.4 Atomic Number and Mass Number • The atomic number is equal to the number of protons in an atom. • On the periodic chart, the atomic number appears above the symbol of an element. 11 Na Atomic Number Symbol
Electrons in An Atom • An atom is electrically neutral; the net charge is zero. • In an atom, the number of protons is equal to the number of electrons. # protons = # electrons • Therefore, the atomic numberis also equal to the number of electrons in a neutral atom.
Mass Number • The mass number gives the total number of protons and neutrons in the nucleus.Mass number = # protons + # neutrons
Atomic Symbol • The atomic symbol represents a particular atom of an element. • The atomic symbol shows the mass numberin the upper left cornerand the atomic number in thelower left corner. • For example, an atom of sodium with atomic number 11 and a mass number 23 has the following atomic symbol:mass number23 Na atomic number11
Information from Atomic Symbols • When we know the atomic symbol of an atom, we can determine the number of protons (p+), neutrons, (n), and electrons (e-). 16 31 65 O P Zn 8 15 30 8 p+ 15 p+ 30 p+ 8 n 16 n 35 n 8 e- 15e- 30 e-
2.5 Isotopes and Atomic Mass 24Mg 25Mg 26Mg 12 12 12
Isotopes • Isotopesare atoms of the same element that have different mass numbers. • Isotopes have the same number of protons, but different numbers of neutrons. • Most elements have two or more isotopes.
Isotopes of Magnesium In naturally occurring atoms of magnesium, there are three isotopes. • 24Mg makes up 78.9% of magnesium atoms. • 25Mg makes up 10.0% and 26Mg makes up 11.1%. 24Mg 25Mg 26Mg 12 12 12
Atomic Mass • Atomic mass is the weighted average mass of all the isotopes of that element. • The atomic mass of each element is compared to 12C, which a mass of 12 amu. • The atomic mass of each element is listed below the symbol of the element on the periodic table.
Atomic Mass of Magnesium • The individual atomic masses of all the isotopes contribute to the atomic mass of Mg. • As a weighted average, the atomic mass is not a whole number.
Calculating Atomic Mass To calculate atomic mass, use the percent(%) abundanceof the isotopes and the mass of each isotope of that element. mass isotope(1) x (%) + mass isotope (2) x (%) + … 100 100
Atomic Mass for Cl • The atomic mass of chlorine is the weighted average of two isotopes 35Cl and 37Cl.
Calculating Atomic Mass for Chlorine • Cl-35 is 75.8 % and Cl-37 is 24.2% of natural chlorine. • Using the given atomic mass of each isotope, calculate the contribution of each isotope to the atomic mass of Cl.35.0 x 75.8 = 26.5 100 37.0 x 24.2 = 8.95 100 • Add together = 35.45 = atomic mass Cl
Electromagnetic Radiation Electromagnetic radiation • Consists of energy particles called photons that travel as waves. • Includes low energy particles that have long wavelengths and high energy particles that have short wavelengths.
Electron Energy Levels • Electrons are arranged in specific energy levels called shells. • The first energy level (n=1) contains electrons that have the lowest energy. • The energy levels are labeled 1, 2, 3, and so on.
Number of Electrons • Electrons of similar energy are grouped in energy levels. • The maximum number of electrons in any energy level is equal to 2n2.n = 1 2(1)2 = 2 n = 2 2(2)2 = 8 n = 3 2(3)2 = 18 n = 4 2(4)2 =32
Order of Electron Filling • The order in which electrons enter and fill the shells for the first 20 electrons is Shell number 1 2 3 4 2e 8e 8e 2e • Although shell 3 can eventually hold 18 electrons, it fills to 8 first.
Electron Shell Arrangement • In the electron shell arrangement, the electrons in each shell of an atom are listed in order of increasing energy. Element Shell 1 2 3He 2 F 2 7 Ne 2 8 Al 2 8 3 Cl 2 8 7