Chapter 3 Atoms and the Periodic Table

Matter What accounts for matters secrets? –Atomists – Democritus –All things are made of Fire – Herclitus –Four Elements – Aristotle

Conservation of Mass and Law of Definite Proportions Robert Boyle (1627–1691): Provided evidence for the atomic nature of matter. –Element - A substance that cannot be chemically broken down further Joseph Priestley (1733– 1804):

Conservation of Mass and Law of Definite Proportions Antoine Lavoisier ( ):

Conservation of Mass Law of Mass Conservation: Mass is neither created nor destroyed in chemical reactions. Hg(NO 3 ) KI → HgI 2 + 2KNO g g → 4.55g g 6.57g = 6.57g

Law of Definite Proportions Law of Definite Proportions: In a unique compound the elements will always be found in the exact same ratio.

Dalton’s Atomic Theory John Dalton (1766–1844): Proposed explanations for the laws of mass conservation and definite proportions. –Postulate 1: Elements are made of atoms –Postulate 2: Atoms of the same element have the same properties (including mass). Atoms of different atoms have different properties –Postulate 3: Compound are comprise of elements joined together in small whole ratios –Postulate 4: Chemical reactions only rearrange the way the atoms are combined

The Structure of Atoms: Electrons Elements are composed of atoms Compounds are composed of atoms of elements in a given ratio What does an atom look like?

The Structure of Atoms Structure of the Atom:

The Structure of Atoms Comparison of Subatomic particles ParticleGramsamuCoulombse Electron x x Proton x x Neutron x

Atomic Number # protons in an atom determines the element –atomic number (Z) - Atomic number is found on the periodic table # electrons = # protons in a neutral atom

Mass Number mass of the atom ≈ # neutrons + # protons –Mass number = # protons + # neutrons –An element may have more than one mass # Isotopes: Atoms with identical atomic numbers, but different mass numbers. Due to different # of neutrons NOT protons

Isotopes and Atomic Weight Atoms of an element that have a different mass are called isotopes

Elements and Atomic Number Symbol# protons# neutronsMass #Atomic ## electrons K

Atomic Mass Atomic Mass: A weighted average of the isotopic masses of an element’s naturally occurring isotopes. –Unit – atomic mass unit (amu)

Example Chlorine has two naturally occurring isotopes: with an abundance of 75.77% and an isotopic mass of amu, and with an abundance of 24.23% and an isotopic mass of amu. What is the atomic mass of chlorine?

Isotopes and Atomic Weight Bromine has two naturally occurring isotopes: 79 Br and 81 Br, calculate the atomic mass of bromine. IsotopeAbundance% 79 Br Br49.31

Problem Atoms X, Y, Z, and R have the following nuclear compositions: Which two are isotopes? –A. X & Y –B. X & R –C. Y & R –D. Z & R –E. X & Z

Electronic Structure The Periodic Table Powerpoint –Elements in a group react similarly Electronic Structure –Atomic Size –Why metals for cations and non-metals anions

Electronic Structure of Atoms Structure based on an accepted quantum mechanical model –Mathematical description of the location in which an electron can be found –Quantum mechanical model – electron cloud can be divided into Shells Subshells Orbitals

Electronic Structure Nucleus Shell – Each Floor Subshell – Row of rooms Orbital - Room 2 beds per room – opposite direction

Electronic Structure of Atoms Shells – layers in which the electrons are grouped around the nucleus –As a layer is added the atomic size increases Shells agree with the period # on periodic table –Differ in energy – requires more energy to remove an electron from a shell closer to the nucleus –Electron capacity – increases with higher shells cause e - can spread out more Shell #1234 e - capacity281832

Electronic Structure of Atoms Subshells –s, p, d, f 1 st shell – only s 2 nd shell – s, p 3 rd shell – s, p, d 4 th shell – s, p, d, f Note: shell has the # of subshells = the shell # 3s electron – an electron is found in the s subshell of the 3 rd shell

Electronic Structure of Atoms Orbitals – Subshells can further be divided into orbitals –regions of space within an atom where the specific electrons are more likely to be found. –Different orbitals have different shapes. Orbitals in s subshells are spherical (a), while orbitals in p subshells are roughly dumbbell shaped (b).

Electronic Structure of Atoms 2 electrons in each orbital with opposite spins

Electronic Structure of Atoms The overall electron distribution within an atom is summarized in Table 3.2 below.

Electron Configurations Electron Configuration: The exact arrangement of electrons in atom’s shells and subshells. Rules to predict electron configuration: 1.Electrons occupy the lowest energy orbitals available first. 2.Each orbital can hold only two electrons, which must be of opposite spin. 3.If two or more orbitals have the same energy, each orbital gets one electron before any orbital gets two.

Electron Configurations Order of orbital energy levels: ► Electrons fill orbitals from the lowest-energy orbitals upward. ► Lower numbered shells fill before higher numbered shells at first. ► Some overlap in energy levels occurs starting with shell 3 and 4.

Electron Configurations ► Electron configurations are described by ► write the shell number ► subshell letter in order of increasing energy. ► number of electrons actually occupying each subshell is indicated by a superscript. ► A graphic representation can be made by indicating each orbital as a line and each electron as an arrow. The head of the arrow indicates the electron spin. ► A shorthand using noble gas configurations is very useful for large atoms.

Periodic Table and Electron Configurations

Electron Configurations

Problem Select the correct electron configuration for sulfur (Z = 16). –A. 1s 2 1p 6 2s 2 2p 6 –B. 1s 2 2s 2 2p 8 3s 2 3p 4 –C. 1s 2 2s 2 2p 8 3s 2 3p 2 –D. 1s 2 2s 2 2p 6 3s 2 3p 4 –E. 1s 2 2s 2 2p 6 3s 2 3d 4

Problem Select the correct electron configuration for Te (Z = 52). –A. [Kr]5s 2 5p 6 4d 8 –B. [Kr]5s 2 5d 10 5p 4 –C. [Kr]5s 2 4d 10 5p 6 –D. [Kr]5s 2 4f 14 –E. [Kr]5s 2 4d 10 5p 4

Problem The electronic structure 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 8 refers to the ground state of –A. Kr –B. Ni –C. Fe –D. Pd –E. none of these choices is correct

Electron Configuration Allows determination of valence e - and core e - Indicates why elements of a group have similar reactivity Determine which element is present by the sum of the superscripts –Ground state atom –Excited state atom

Optional Homework Text – 3.31, 3.32, 3.33, 3.44, 3.46, 3.48, 3.50, 3.52, 3.56, 3.70, 3.72, 3.74, 3.76, 3.78, 3.82, 3.84, 3.86, 3.96, 3.100, 3.106, 3.108, 3.110, Chapter 3 Homework – from website