1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 2 Lecture Outline Prepared by Jennifer N. Robertson-Honecker West Virginia University

2 Atoms and the Periodic Table Elements An element is a pure substance that cannot be broken down into simpler substances by a chemical reaction. Each element is identified by a one- or two-letter symbol. Elements are arranged in the periodic table. The position of an element in the periodic table tells us much about its chemical properties.

3 Atoms and the Periodic Table Elements

4 Atoms and the Periodic Table

5 Atoms and the Periodic Table Metals, Nonmetals, and Metalloids Metals: are located on the left side of the periodic table usually exist as shiny solids are good conductors of heat and electricity are solids at room temperature, except for mercury (Hg), which is a liquid The elements in the periodic table are divided into three groups—metals, nonmetals, and metalloids.

6 Nonmetals: are located on the right side of the periodic table usually do not have a shiny appearance are usually poor conductors of heat and electricity can be solids, liquids, or gases at room temperature Atoms and the Periodic Table Metals, Nonmetals, and Metalloids solidliquidgas sulfur carbon brominenitrogen oxygen

7 Atoms and the Periodic Table Metals, Nonmetals, and Metalloids Metalloids: are located on the solid line that starts at boron (B) and angles down towards astatine (At) have properties intermediate between metals and nonmetals are represented by only seven elements: boron (B) silicon (Si) germanium (Ge) arsenic (As) antimony (Sb) tellurium (Te) astatine (At)

Focus on the Human Body The Elements of Life 8

9 Atoms and the Periodic Table Compounds Compound: a pure substance formed by chemically combining two or more elements together. element symbols to show the identity of the elements forming a compound A chemical formula consists of: subscripts to show the ratio of atoms in the compound H2OH2O 2 H atoms1 O atom C3H8C3H8 3 C atoms8 H atoms H2OH2OC3H8C3H8

10 Atoms and the Periodic Table Compounds Compounds can be drawn many ways: Different elements are represented by different colors:

11 Structure of the Atom All matter is composed of the same basic building blocks called atoms. Atoms are composed of three subatomic particles:

12 Structure of the Atom Nucleus: location of protons and neutrons dense core of the atom most of the mass of the atom resides here Electron cloud: location of electrons comprises most of the atom’s volume

13 Structure of the Atom Atomic Number From the periodic table: 3 Li Atomic number (Z) is the number of protons in the nucleus. Every atom of a given element has the same number of protons in the nucleus. Different elements have different atomic numbers. Every atom of a given element has the same atomic number. A neutral atom has no net overall charge, so Z = number of protons = number of electrons

14 Mass Number the number of protons (Z) + the number of neutrons Mass number (A) =

15 Isotopes Isotopes, Atomic Number, and Mass Number Isotopes are atoms of the same element that have a different number of neutrons Cl Mass number (A) Atomic number (Z) # of protons = 1717 # of electrons = 1717 # of neutrons = 35 – 1737 – 17 = Cl

16 Isotopes Atomic Weight The atomic weight is the weighted average of the masses of the naturally occurring isotopes of a particular element reported in atomic mass units. From the periodic table: 82 Pb atomic number (Z) element symbol atomic weight (amu)

17 The Periodic Table Basic Features of the Periodic Table A row in the periodic table is called a period, and a column in the periodic table is called a group. consist of the two columns on the far left and the six columns on the far right of the periodic table the groups are numbered 1A–8A contained in the 10 short columns in the middle these groups are numbered 1B–8B Main group elements: Transition metal elements: Inner transition elements: consist of the lanthanides and actinides no group numbers are assigned

18 The Periodic Table Basic Features of the Periodic Table

19 The Periodic Table Characteristics of Groups 1A and 2A Elements that comprise a particular group have similar chemical properties. Group Number Group Name Properties of Both Groups 1AAlkali metals 2A Alkaline earth elements soft and shiny metals low melting points good conductors of heat and electricity react with water to form basic solutions

20 The Periodic Table Characteristics of Groups 7A and 8A Group Number Group Name Properties 7AHalogens 8A Noble gases exist as two atoms joined together very reactive; combine with many other elements to form compounds very stable rarely combine with any other elements

The chemistry of an element is determined by the number of electrons in an atom. 21 Electronic Structure Electrons do not move freely in space; rather they occupy specific energy levels. The regions occupied by electrons are called principal energy levels or shells (n). The shells are numbered n = 1, 2, 3, etc. Electrons in lower numbered shells are closer to the nucleus and are lower in energy. Electrons in higher numbered shells are further from the nucleus and are higher in energy.

22 Electronic Structure Shells Shells with larger numbers (n) are farther from the nucleus, have a larger volume, and therefore, can hold more electrons. The distribution of electrons in the first four shells: Shell (n) Number of Electrons in a Shell increasing energy increasing number of electrons

23 Electronic Structure Subshells and Orbitals Shells are divided into subshells, identified by the letters s, p, d, and f. The subshells consist of orbitals. An orbital is a region of space where the probability of finding an electron is high. Each orbital can hold two electrons. Subshell Number of Orbitals s p d f increasing energy

24 Electronic Structure Subshells and Orbitals

25 Electronic Structure Orbital Shapes The s orbital has a spherical shape. The p orbital has a dumbbell shape.

26 Electron Configuration The electron configuration describes how the electrons are arranged in an atom’s orbitals. The lowest energy arrangement is called the ground state. Rules to Determine the Ground State Electronic Configuration of an Atom Rule [1] Electrons are placed in the lowest energy orbitals beginning with the 1s orbital. An orbital closer to the nucleus is lower in energy. Within a shell, orbital energies increase in the following order: s, p, d, f. These guidelines result in the following order of energies 1s, 2s, 2p, 3s, 3p. Rule [2] Each orbital holds a maximum of 2 electrons.

27 Electron Configuration Rules to Determine the Ground State Electronic Configuration of an Atom

28 Electron Configuration First-Row Elements (Period 1) H (Z = 1) 1 electron 1s11s1 He (Z = 2) 2 electrons 1s21s2 Element Electron Configuration

29 Electron Configuration Second-Row Elements (Period 2) Li (Z = 3) 3 electrons 1s22s11s22s1 C (Z = 6) 6 electrons 1s22s22p21s22s22p2 Element Electron Configuration Ne (Z = 10) 10 electrons 1s22s22p61s22s22p6

30 Valence Electrons The valence shell is the outermost shell (the highest value of n). Be 1s22s21s22s2 Cl 1s22s22p63s23p51s22s22p63s23p5 valence shell: n = 2 # of valence electrons = 2 valence shell: n = 3 # of valence electrons = 7 The electrons in the valence shell are called valence electrons. The chemical properties of an element depend on the most loosely held electrons, which are found in the valence shell.

31 Valence Electrons Elements in the same group have similar electron configurations. Elements in the same group have the same number of valence electrons. The group number, 1A–8A, equals the number of valence electrons for the main group elements. The exception is He, which has only 2 valence electrons. The chemical properties of a group are similar because these elements contain the same electronic configuration of valence electrons.

32 Valence Electrons Main Group Elements Group number: Period 1: Period 2: Period 3: 1A2A3A4A5A 6A 7A8A Li 2s 1 Be 2s 2 B2s22p1B2s22p1 C2s22p2C2s22p2 N2s22p3N2s22p3 O2s22p4O2s22p4 F2s22p5F2s22p5 Ne 2s 2 2p 6 Na 3s 1 Mg 3s 2 Al 3s 2 3p 1 Si 3s 2 3p 2 P3s23p3P3s23p3 S3s23p4S3s23p4 Cl 3s 2 3p 5 Ar 3s 2 3p 6 H1s1H1s1 He 1s 2

33 Valence Electrons Electron-Dot Symbols Dots representing valence electrons are placed on the four sides of an element symbol. Each dot represents one valence electron. For 1–4 valence electrons, single dots are used. With > 4 valence electrons, the dots are paired. Element: # of Valence electrons: Electron-dot symbol: H 1 H C 4 C O 6 O Cl 7

34 Periodic Trends Atomic Size Increases The size of atoms increases down a column, as the valence e − are farther from the nucleus. Decreases The size of atoms decreases across a row, as the number of protons in the nucleus increases. The increasing # of protons pulls the e − closer to the nucleus, making the atoms smaller.

35 Periodic Trends Ionization Energy Decreases The ionization energy is the energy needed to remove an electron from a neutral atom. Na + energy  Na + + e – Ionization energies decrease down a column as the valence e − get farther away from the positively charged nucleus. Increases Ionization energies increase across a row as the number of protons in the nucleus increases.