Atoms and the Periodic Table CHE 101 Sleevi Chapter 2 Atoms and the Periodic Table CHE 101 Sleevi

Atoms and the Periodic Table Element Substance that cannot be broken down into simpler substances by a chemical reaction Identified by a one or two letter symbol 1st letter capitalized 2nd letter, if present, lowercase Position on the periodic table based on chemical properties

Atoms and the Periodic Table 3 3

The Periodic Table http://www.theodoregray.com/PeriodicTable/index.html http://www.rsc.org/chemsoc/visualelements/pages/pertable_fla.htm

Elements and the Periodic Table Metals Left of the stair-step line on the periodic table Shiny (lustrous) Malleable Solids at room temperature except Hg which is a liquid Good conductors of heat and electricity

Elements and the Periodic Table Nonmetals Right of the stair-step line on the periodic table Usually not shiny Can be solids, liquids or gases at room temperature (Br is the only liquid nonmetal) Poor conductors of heat and electricity

Elements and the Periodic Table Metalloids Elements that abut the stair-step line on the periodic table Have properties that are intermediate between metals and nonmetals Silicon is brittle, but conducts electricity, is a shiny blackish silver color

Elements and the Periodic Table Compounds Substance formed by chemically combining two or more elements together Use chemical symbols to describe the compound Symbols identify the types of elements (atoms) in the compound Subscripts show the ratio of the number of each type of atom in the smallest representative particle of the element

Chemical Formulas Examples H2O one molecule contains two H atoms one O atom C3H6 one molecule contains three C atoms six H atoms

Representations of Chemical Compounds Typical colors used for atoms:

Elements of Biological Interest Building block elements Comprise 96% of mass of human body C, O, H, N Major nutrients (> 100 mg/day) K, Na, Cl, Mg, S, Ca, P Trace elements (< 15 mg/day) As, B, Cr, Co, Cu F, I, Fe, Mn, Mo, Ni, Se, Si, Zn

Other Elements of Interest Most abundant elements on Earth O, Si, Al, Fe, Ca, Na, K, Mg, H, Ti Make up 98.9% of mass of the crust, ocean and atmosphere

Atomic Structure Since the late 19th Century, experimental evidence has determined the atom is composed of particles Particle Discovery Proton 1886 - Goldstein Electron 1897 - Thomson Neutron 1932 - Chadwick

Characteristics of Fundamental Subatomic Particles Symbol Charge Mass (g) Relative Mass (amu) Location Proton p +1 1.67 x 10-24 1 Nucleus Neutron n Electron e- -1 9.07 x 10-28 1/1836 OutsideNucleus 14

Structure of the Atom Nucleus: Electron cloud: location of protons and neutrons dense core of the atom location of most of the atom’s mass location of electrons comprises most of the atom’s volume 15 15

Atomic Structure Atoms are neutral (#p = #e-) Nucleus is central, dense core of the atom Most of the mass of the atom is in the nucleus Mass of electrons negligible compared to mass of nucleus Chemical properties dependent upon the electrons

Identification of Atoms Atomic number (Z) Number of protons Identifies the element Mass number (A) = # of protons + # of neutrons In neutral atom: # of protons = # of electrons

Structure of the Atom Atomic Number From the periodic table: Atomic number (Z) is the number of protons in the nucleus. 3 Li Every atom of a given element has the same atomic number. Every atom of a given element has the same number of protons in the nucleus. Different elements have different atomic numbers. 18 18

Quick Review Particle Symbol Charge Relative Mass Location in Atom Purpose Proton Neutron Electron

Isotopes 6C Chemically alike Atoms with same atomic number but different mass number (different number of neutrons Chemically alike 6C 12 Z = atomic number A = mass number Z = # p = 6 A = # p + # n = 12 20

element name – mass number Isotopes Isotopes often listed as: element name – mass number carbon-14 nitrogen-14 uranium-238 C-12 Pb-207 Write the chemical symbols for these isotopes, including both atomic number and mass number 21

Data on the Periodic Table atomic number (Z) 6 C 12.01 element symbol atomic weight (amu) Note: atomic weight also called atomic mass or average atomic mass Mass number does NOT appear on the periodic table

1 amu = 1/12 the mass of a C-12 atom Average Atomic Mass Weighted average of the mass of the stable, naturally occurring isotopes of an element Ave at mass = Σ (rel. abund. * isotope mass) Mass units for individual atoms in atomic mass units (1 amu) 1 amu = 1/12 the mass of a C-12 atom

Calculating the Average Atomic Mass Data needed Number of isotopes Relative abundance of each isotope Isotope mass Calculation Weighted average Sum of products of rel abundance and isotope mass

Calculating the Average Atomic Mass Example

The Modern Periodic Table Based on work of Mendeleev, 1869 about 65 known elements arranged elements based on trends in physical and chemical properties left spaces for other elements, not yet discovered generally organized according to increasing atomic weight 26

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Modern Periodic Table Numerous people worked on periodic table at this time Henry Moseley, British Physicist, 1913 determined nuclear charge of atoms (Z) arranged elements in order of increasing atomic number 28

Periodic Law When elements are arranged in order of increasing atomic number, there is a periodic pattern in their physical and chemical properties 29

Structure of the Periodic Table Group Vertical columns Number appears above the column Period Row May or not have written number 1st period contains H and He

Group Names Main group elements Transition Metal elements Also called representative elements Designated by Group numbers 1A – 8A Transition Metal elements Short columns in the middle (“short stack”) Designated by Group numbers ending in B Inner transition elements Lanthanide and actinide series No group numbers

Periodic Table of the Elements Noble Gases Periodic Table of the Elements Alkaline Earth Metals 1A 2A 3A 4A 5A 6A 7A 8A Halogens Transition Metals Alkali Metals 3B 4B 5B 6B 7B 8B 1B 2B Metalloids Inner Transition Metals 32

Group Names of the Main Group Elements Group Number Group Name Properties of Both Groups 1A Alkali Metals Soft, shiny metals Low melting points Good conductors (heat, electricity) React with water to form basic solutions 2A Alkaline Earth Metals

Group Names of the Main Group Elements Group Number Group Name Properties 7A Halogens Exist as diatomic molecules Very reactive 8A Noble gases Exist as monatomic species Very stable Rarely combine with other elements

Location of the Elements Since periodic table is a grid, elements can be located by “coordinates” of their group number and period number name the element in Group 2A, period 3 name the element in Group 5B, period 4 Element properties can be identified by knowing its group name the group for Mg name the group for Ne 35

Modern Atomic Theory and Electron Configurations 1911 – Rutherford’s Gold Foil Expt 1913 – Bohr proposed fixed orbits for electrons based on energy studied hydrogen emission spectrum Bohr’s model did not resolve all observations Early 1900’s – Birth of Quantum Mechanics 1926 – Schrödinger proposed quantum mechanical model of the atom 36

Quantum Mechanical Model of the Atom Principal energy levels (shells) correspond to the discrete energy levels in the atom that can be occupied by electrons designated by quantum number n (n = 1, 2, 3, 4, …) contain sublevels quantum number n designates number of sublevels at that energy level Sublevels (subshells) correspond to orbital type within a principal energy level (s, p, d, f) 37

Orbitals Solution to the Schrödinger equation Shape describes the probability of where electron will be found in space, at that energy Overlay the nucleus Increase in size as the principle energy level increases Contain no more than 2 electrons 38

Electronic Structure Orbital Shapes The s orbital has a spherical shape. The p orbital has a dumbbell shape. 39 39

Sublevels: Orbital Types & Shapes spherical 1 possible s orbital at a given PEL p dumbbell 3 possible p orbitals at a given PEL px, py, pz d more complex, multiple lobes 5 possible d orbitals at a given PEL 40

Energy Levels in an Atom Principal Energy Level (shells) Sublevels (subshells) 1 s 2 s, p 3 s, p, d 4 s, p, d, f 41

Orbitals and Electrons by Sublevel Max # Electrons s 1 2 p 3 6 d 5 10 f 7 14 42

Max Number of Electrons by Principal Energy Level Sublevels Max # Electrons 1 s 2 s, p 2 + 6 = 8 3 s, p, d 2 + 6 + 10 = 18 4 s, p, d, f 2 + 6 + 10 +14 = 32 43

Electronic Structure Shells Shells with larger numbers (n) are farther from the nucleus, have a larger volume, and can therefore hold more electrons. The distribution of electrons in the first four shells: Number of Electrons in a Shell Shell (n) 4 32 3 18 increasing number of electrons increasing energy 2 8 1 2 44 44

Electron Configurations Arrangement of electrons around the nucleus Based on set of rules that comes from Quantum Mechanical model of the atom 45

Electron Configurations Rules determine how orbitals are filled, based on number of electrons in the atom Aufbau Principle Pauli Exclusion Principle Hund’s Rule 46

Aufbau Principle Electrons enter orbitals of lowest energy first Filling order: 1s 2s 2p 3s 3p 4s 3d 4p 5s ….. Number in front = quantum number (PEL) Letter designates sublevel (orbital type) Maximum number of electrons depends upon the orbital type 47

Aufbau Diagram 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 6f 48

Pauli Exclusion Principle An orbital can contain 0, 1, or 2 electrons Electrons have a property called spin When there are two electrons in one orbital they have opposite spin 49

Hund’s Rule When electrons occupy orbitals of equal energy, one electron enters each orbital with parallel spin a. b. c. 50

Following the rules… Elements through Vanadium follow these rules Most elements after that follow the rules There are exceptions 51

Writing Configurations Diagram Use horizontal lines for orbitals, Arrows for electrons, Direction of arrows for spin Label rows with PEL and orbital designation (1s, 2s, 2p, etc.) Follow Aufbau Rule, Pauli Exclusion Principle, Hund’s rule 52

Examples Lecture Problems 53

Electron Configuration Shorthand Write PEL and orbital type as number, letter Use superscript for number of electrons in the orbital 1s22s22p3 Element can be identified by adding up the superscripts (# electrons) 54

Mapping Aufbau Diagram to the Periodic Table Electrons enter s orbitals (1A, 2A) Electrons enter p orbitals (3A – 8A) Electrons enter d orbitals (Transition metals) Electrons enter f orbitals (Inner transition metals) Principal energy level for s and p given by the row number 55

Periodic Table of the Elements 56

Electron Configurations and the Periodic Table FIGURE 2.9 The Blocks of Elements in the Periodic Table

Electron Configurations Element Symbol Shorthand Notation Noble Gas Notation Li 1s22s1 [He] 2s1 Na 1s22s22p63s1 [Ne] 3s1 K 1s22s22p63s23p64s1 [Ar] 4s1 Rb 1s22s22p63s23p64s24p65s1 [Kr]5s1 58

Unpaired Electrons

Practice!! Lecture Problem 60

Valence Electrons Outermost electrons Highest occupied principle energy level (largest quantum number) Number of valence electrons = group number for the A groups Determine the chemical properties of the elements Determine number and type of bonds 61

Valence Configurations

More Practice! Lecture Problems 63

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: H C O Cl # of Valence electrons: 1 4 6 7 Electron-dot symbol: H C O Cl 64 64

Practice! Draw Lewis dot structures for reach of the following: S P Sr C Br Kr Na Al

Periodic Trends Properties of the elements are dependent upon their location on the periodic table (periodic law) Properties have trends with respect to location of elements on periodic table Atomic Size Ionization Energy 66

Periodic Trends Atomic Size The size of atoms increases down a column, as the valence e− are farther from the nucleus. Increases 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. 67 67

Periodic Trends Ionization Energy The ionization energy is the energy needed to remove an electron from a neutral atom. Na + energy  Na+ + e– Decreases 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. 68 68

Examples! Arrange the atoms in order of increasing size B, C, Ne F, S, Al Kr, Ne, Xe Ca, Mg, Be

Examples! Arrange the atoms in order of increasing ionization energy P, Si, S Ne, Kr, Ar C, F, Be Ca, Al, N