Chapter 4 Atoms and the Periodic Table

Atomic Structure What are Atoms? Democritus (Greece, 400BC) named the smallest bit of matter unable to be divided the ATOM John Dalton John Dalton (1808) proposed the Atomic Theory: John Dalton Atoms are the building blocks of matter Atoms are the building blocks of matter Atoms of given elements are exactly the same Atoms of given elements are exactly the same Atoms of different elements are different Atoms of different elements are differentExamples:

Atomic Composition Atomic CompositionProtons: In the nucleus In the nucleus Positive charge Positive charge Mass of about 1 amu (atomic mass unit) Mass of about 1 amu (atomic mass unit) ElectronElectron: Electron Outside the nucleus Outside the nucleus Negative charge Negative charge Mass is about 0 amu Mass is about 0 amuNeutron: In the nucleus In the nucleus No charge No charge Mass is about 1 amu Mass is about 1 amu

Atom Models Bohr Model Bohr Model (1913): electrons move in set paths around the nucleus much like the planets in the solar system solar system Bohr Model solar system An Electron has a certain energy determined by its path Electrons can be in only one energy level but can move to higher and lower energy levels by gaining or losing energy

Atom Models cont. Many atomic models were proposed until the widely accepted wave model of today Electrons do not have definite paths but behave more like waves on vibrating strings rather than particles An electron’s exact location cannot be determined Electrons exist in orbitals within energy levels Electrons in the outermost energy levels are called valence electrons – there are between 1 and 8

Sect. 2:Touring the Periodic Table Periodic TablePeriodic Table Organization Organization Similar elements are grouped together Periodic law states that similar properties occur in patterns Elements are represented by symbols (Gold – Au, Nitrogen – N) Elements are in order of atomic number (number of protons in the nucleus) PeriodsPeriods – rows (across) Periods GroupsGroups – columns (up and down) Groups

What do the numbers mean? Atomic number: Each element has its own atomic number Each element has its own atomic number number of protons in the nucleus number of protons in the nucleus For a neutral atom, also the number of electrons For a neutral atom, also the number of electrons Mass number: Round the atomic mass Round the atomic mass Mass of nucleus=protons +neutrons Mass of nucleus=protons +neutrons IsotopeIsotope: Isotope different ‘versions’ of an element that contains a different number of neutrons different ‘versions’ of an element that contains a different number of neutrons an average of all these occurring isotopes in nature results in the atomic mass listed on the periodic table an average of all these occurring isotopes in nature results in the atomic mass listed on the periodic table

How many subatomic particles in an atom? Protons: the atomic number Electrons: the atomic number Neutrons: mass number – atomic number Examples: Carbon Carbon Hydrogen Hydrogen Potassium Potassium

Section 3: Element Families Metals: left of staircase, shiny, ductile, malleable, and good conductors of heat and electricity Alkali MetalsAlkali Metals: Alkali Metals Group 1 (1A), Group 1 (1A), one valence electron one valence electron Soft and shiny Soft and shiny React with water React with water Alkaline Earth MetalsAlkaline Earth Metals: Alkaline Earth Metals Group 2 (2A), 2 valence electrons Group 2 (2A), 2 valence electrons Transition Metals: Groups 3-12 (IIIB-IIB), Groups 3-12 (IIIB-IIB), Groups 3-12 (IIIB-IIB), Groups 3-12 (IIIB-IIB), 1 or 2 valence electrons 1 or 2 valence electrons Some of these metals can form more than one cation Some of these metals can form more than one cation

Families (cont) Nonmetals: right side of the table Nonmetals: right side of the table HalogensHalogens: Halogens Group 17 (VIIA), Group 17 (VIIA), Group 17 (VIIA Group 17 (VIIA 7 valence electrons 7 valence electrons Highly reactive Highly reactive Form halides (salts) with metals Form halides (salts) with metals Noble gases Noble gases Group 18(VIIIA), 8 valence electrons (He 2) Group 18(VIIIA), 8 valence electrons (He 2) Inert, nonreactive Inert, nonreactiveMetalloids: Located along the staircase Located along the staircase Have characteristics of metals and nonmetals Have characteristics of metals and nonmetals NOT aluminum NOT aluminum

Chapter 4 section 4: What is a Mole!? Counting: dozen, ream, gross, mole Mole = x particles In chemistry, one mole = x atoms Conversion factor = 1 1kg/ 1000g, 365 days/ 1 year, 365 days/8760hours, 1 mol Mg/ g or g/1 mol 1kg/ 1000g, 365 days/ 1 year, 365 days/8760hours, 1 mol Mg/ g or g/1 mol

Example of unit conversions: How old am I, in seconds? Start with given information. End with correct units. Remember the identity element of algebra.

Amount to Mass: 1.Write the given over the number one 50 moles of iron/1 50 moles of iron/1 2. Multiply by the molar mass of the element: ---g/1 mol (50 moles of iron/1) x ( g of Fe/ 1 mol of iron) 3. Check your units: grams

Mass to amount: 1.Write the given mass over the number one: 98 g of carbon/1 2.Multiply by the molar mass: 1 mol/---g (98 g of carbon/1) x (1mol carbon/12 g of carbon) 3. Check your units: moles