Chapter 2: The Components of Matter 2.5 The Atomic Theory Today 2.6 Elements: A First Look at the Periodic Table 2.7 Compounds: Introduction to Bonding

Clicker question #7 The definition of an element is: A substance that consists of only one type of atom. A substance that can be broken down into simpler substances by physical or chemical means. A substance that consists of multiple types of atoms. A structure that consists of two or more atoms that are chemically bound together

Clicker question #7 The definition of an element is: A substance that consists of only one type of atom. A substance that can be broken down into simpler substances by physical or chemical means. A substance that consists of multiple types of atoms. A structure that consists of two or more atoms that are chemically bound together

General features of the atom today. The atom is an electrically neutral, spherical entity composed of a positively charged central nucleus surrounded by one or more negatively charged electrons. The atomic nucleus consists of protons and neutrons.

Properties of the Three Key Subatomic Particles Charge Mass Location in the Atom Nucleus Outside Name(Symbol) Electron (e-) Neutron (n0) Proton (p+) Relative 1+ 1- Absolute(C)* +1.60218x10-19 -1.60218x10-19 Relative(amu)† 1.00727 1.00866 0.00054858 Absolute(g) 1.67262x10-24 1.67493x10-24 9.10939x10-28 * The coulomb (C) is the SI unit of charge. † The atomic mass unit (amu) equals 1.66054x10-24 g.

Atomic Symbols, Isotopes, Numbers X The Symbol of the Atom or Isotope Z X = Atomic symbol of the element A = mass number; A = Z + N Z = atomic number (the number of protons in the nucleus) N = number of neutrons in the nucleus Isotope = atoms of an element with the same number of protons, but a different number of neutrons

Sample Problem 2.2 Determining the Number of Subatomic Particles in the Isotopes of an Element PROBLEM: How many protons, neutrons, and electrons are in the following elements. What element symbols do Q and X represent? 115 Q 4120 X

Clicker question #8 Given 13153 Y. What element symbol does Y represent? Na I Pt Cs

Clicker question #8 Given 13153 Y. What element symbol does Y represent? Na I Pt Cs

Sample Problem 2.3 Calculating the Atomic Mass of an Element Definition: amu or Da (atomic mass unit or Dalton) = 1/12 mass of 12C atom. PROBLEM: Silver(Ag: Z = 47) has 46 known isotopes, but only two occur naturally, 107Ag and 109Ag. Given the following mass spectrometric data, calculate the atomic mass of Ag: Isotope Mass(amu) Abundance(%) 107Ag 109Ag 106.90509 108.90476 51.84 48.16

The Modern Reassessment of the Atomic Theory 1. All matter is composed of atoms. The atom is the smallest body that retains the unique identity of the element. 2. Atoms of one element cannot be converted into atoms of another element in a chemical reaction. Elements can only be converted into other elements in nuclear reactions. 3. All atoms of an element have the same number of protons and electrons, which determines the chemical behavior of the element. Isotopes of an element differ in the number of neutrons, and thus in mass number. A sample of the element is treated as though its atoms have an average mass. 4. Compounds are formed by the chemical combination of two or more elements in specific ratios.

The modern periodic table. Similar chemical properties

The modern periodic table. Alkali metals

The modern periodic table. Alkaline earth metals

The modern periodic table. Halogens

The modern periodic table. Noble gases

Clicker question #9 Using the periodic table, do you think Na and Cl have similar chemical properties? Yes, I think they have similar chemical properties. No, I do not think they have similar chemical properties. I can not tell from the periodic table whether they have similar chemical properties. This is a stupid question.

Clicker question #9 Using the periodic table, do you think Na and Cl have similar chemical properties? Yes, I think they have similar chemical properties. No, I do not think they have similar chemical properties. I can not tell from the periodic table whether they have similar chemical properties. This is a stupid question.

Bonding – ionic compounds Formed from – the transfer of electrons from the atoms of one element to those of another Ions – charged particles Cation – positively charged ion Anion – negatively charged ion Ionic compound formation animation

Sample Problem 2.4 Predicting the Ion and Element Forms PROBLEM: What monatomic ions do the following elements form? (a) Sulfur (b) Rubidium (c) Barium

Formation of a covalent bond between two H atoms. Covalent bonds form when elements share electrons, which usually occurs between nonmetals.

Elements that occur as molecules. (1) (2) (13) (14) (15) (16) (17) (18) H2 N2 O2 F2 P4 S8 Cl2 Se8 Br2 I2 diatomic molecules tetratomic molecules octatomic molecules

Entities in covalent and ionic substances Most covalent substances consist of molecules No molecules exist in a sample of an ionic compound

Elements that are polyatomic. A polyatomic ion