the atom 1) nucleonsnucleons 2) isotopesisotopes 6) electron configuationelectron configuation 7)...

The Atom

1) Nucleons

2) Isotopes

6) Electron Configuation

7) Development of the Atomic Model

(c) 2006, Mark Rosengarten

Nucleons

Protons: +1 each, determines identity of element, mass of 1 amu, determined using atomic number, nuclear charge

Neutrons: no charge, determines identity of isotope of an element, 1 amu, determined using mass number - atomic number (amu = atomic mass unit)

3216S and 33

16S are both isotopes of S

S-32 has 16 protons and 16 neutrons S-33 has 16 protons and 17 neutrons All atoms of S have a nuclear charge of +16 due to the 16

protons.

Isotopes

Atoms of the same element MUST contain the same number of protons.

Atoms of the same element can vary in their numbers of neutrons, therefore many different atomic masses can exist for any one element. These are called isotopes.

The atomic mass on the Periodic Table is the weight-average atomic mass, taking into account the different isotope masses and their relative abundance.

Rounding off the atomic mass on the Periodic Table will tell you what the most common isotope of that element is.

Weight-Average Atomic Mass

WAM = ((% A of A/100) X Mass of A) + ((% A of B/100) X Mass of B) + …

What is the WAM of an element if its isotope masses and abundances are:

– X-200: Mass = 200.0 amu, % abundance = 20.0 %

– X-204: Mass = 204.0 amu, % abundance = 80.0%

– amu = atomic mass unit (1.66 × 10-27 kilograms/amu)


Most Common Isotope

The weight-average atomic mass of Zinc is 65.39 amu. What is the most common isotope of Zinc? Zn-65!

What are the most common isotopes of:

– Co Ag– S Pb

FACT: one atomic mass unit (1.66 × 10-27 kilograms) is defined as 1/12 of the mass of an atom of C-12.

This method doesn’t always work, but it usually does. Use it for the Regents exam.


Electron Configuration

Basic Configuration Valence Electrons Electron-Dot (Lewis Dot) Diagrams Excited vs. Ground State What is Light?


Basic Configuration

The number of electrons is determined from the atomic number.

Look up the basic configuration below the atomic number on the periodic table. (PEL: principal energy level = shell)

He: 2 (2 e- in the 1st PEL) Na: 2-8-1 (2 e- in the 1st PEL, 8 in the 2nd and 1 in the

3rd) Br: 2-8-18-7 (2 e- in the 1st PEL, 8 in the 2nd, 18 in the

3rd and 7 in the 4th)


Valence Electrons

The valence electrons are responsible for all chemical bonding.

The valence electrons are the electrons in the outermost PEL (shell).

He: 2 (2 valence electrons) Na: 2-8-1 (1 valence electron) Br: 2-8-18-7 (7 valence electrons)

The maximum number of valence electrons an atom can have is EIGHT, called a STABLE OCTET.


Electron-Dot Diagrams

The number of dots equals the number of valence electrons.

The number of unpaired valence electrons in a nonmetal tells you how many covalent bonds that atom can form with other nonmetals or how many electrons it wants to gain from metals to form an ion.

The number of valence electrons in a metal tells you how many electrons the metal will lose to nonmetals to form an ion. Caution: May not work with transition metals.

EXAMPLE DOT DIAGRAMS


Example Dot Diagrams

Carbon can also have this dot diagram, which ithas when it forms organic compounds.


Excited vs. Ground State

Configurations on the Periodic Table are ground state configurations.

If electrons are given energy, they rise to higher energy levels (excited state).

If the total number of electrons matches in the configuration, but the configuration doesn’t match, the atom is in the excited state.

Na (ground, on table): 2-8-1 Example of excited states: 2-7-2, 2-8-0-1, 2-6-3


Development of the Atomic Model Thompson Model Rutherford Gold Foil Experiment and Mode

l Bohr Model Quantum-Mechanical Model


Thompson Model

The atom is a positively charged diffuse mass with negatively charged electrons stuck in it.


Rutherford Model

The atom is made of a small, dense, positively charged nucleus with electrons at a distance, the vast majority of the volume of the atom is empty space.

Alpha particles shotat a thin sheet of goldfoil: most go through(empty space). Somedeflect or bounce off(small + chargednucleus).


Bohr Model

Electrons orbit around the nucleus in energy levels (shells). Atomic bright-line spectra was the clue.


Quantum-Mechanical Model

Electron energy levels are wave functions. Electrons are found in orbitals, regions of space where an

electron is most likely to be found. You can’t know both where the electron is and where it is

going at the same time. Electrons buzz around the nucleus like gnats buzzing

around your head.


Types of Matter

Substances (Homogeneous)– Elements (cannot be decomposed by chemical

change): Al, Ne, O, Br, H– Compounds (can be decomposed by chemical

change): NaCl, Cu(ClO3)2, KBr, H2O, C2H6

Mixtures– Homogeneous: Solutions (solvent + solute)– Heterogeneous: soil, Italian dressing, etc.


Elements A sample of lead atoms (Pb). All

atoms in the sample consist of lead, so the substance is homogeneous.

A sample of chlorine atoms (Cl). All atoms in the sample consist of chlorine, so the substance is homogeneous.


Compounds Lead has two charges listed, +2

and +4. This is a sample of lead (II) chloride (PbCl2). Two or more elements bonded in a whole-number ratio is a COMPOUND.

This compound is formed from the +4 version of lead. This is lead (IV) chloride (PbCl4). Notice how both samples of lead compounds have consistent composition throughout? Compounds are homogeneous!


Mixtures A mixture of lead atoms and

chlorine atoms. They exist in no particular ratio and are not chemically combined with each other. They can be separated by physical means.

A mixture of PbCl2 and PbCl4 formula units. Again, they are in no particular ratio to each other and can be separated without chemical change.


The Periodic Table

Metals Nonmetals Metalloids Chemistry of Groups Electronegativity Ionization Energy


Metals

Have luster, are malleable and ductile, good conductors of heat and electricity

Lose electrons to nonmetal atoms to form positively charged ions in ionic bonds

Large atomic radii compared to nonmetal atoms Low electronegativity and ionization energy Left side of the periodic table (except H)


Nonmetals

Are dull and brittle, poor conductors Gain electrons from metal atoms to form negatively

charged ions in ionic bonds

Share unpaired valence electrons with other nonmetal atoms to form covalent bonds and molecules

Small atomic radii compared to metal atoms High electronegativity and ionization energy Right side of the periodic table (except Group 18)


Metalloids

Found lying on the jagged line between metals and nonmetals flatly touching the line (except Al and Po).

Share properties of metals and nonmetals (Si is shiny like a metal, brittle like a nonmetal and is a semiconductor).


Chemistry of Groups

Group 1: Alkali Metals Group 2: Alkaline Earth Metals Groups 3-11: Transition Elements Group 17: Halogens Group 18: Noble Gases

Diatomic Molecules


Group 1: Alkali Metals

Most active metals, only found in compounds in nature

React violently with water to form hydrogen gas and a strong base: 2 Na (s) + H2O (l) 2 NaOH (aq) + H2 (g)

1 valence electron Form +1 ion by losing that valence electron Form oxides like Na2O, Li2O, K2O


Group 2: Alkaline Earth Metals

Very active metals, only found in compounds in nature

React strongly with water to form hydrogen gas and a base:

– Ca (s) + 2 H2O (l) Ca(OH)2 (aq) + H2 (g)

2 valence electrons Form +2 ion by losing those valence electrons Form oxides like CaO, MgO, BaO


Groups 3-11: Transition Metals

Many can form different possible charges of ions If there is more than one ion listed, give the charge as a

Roman numeral after the name Cu+1 = copper (I) Cu+2 = copper (II) Compounds containing these metals can be colored.


Group 17: Halogens

Most reactive nonmetals React violently with metal atoms to form halide

compounds: 2 Na + Cl2 2 NaCl

Only found in compounds in nature Have 7 valence electrons Gain 1 valence electron from a metal to form -1

ions Share 1 valence electron with another nonmetal

atom to form one covalent bond.


Group 18: Noble Gases

Are completely nonreactive since they have eight valence electrons, making a stable octet.

Kr and Xe can be forced, in the laboratory, to give up some valence electrons to react with fluorine.

Since noble gases do not naturally bond to any other elements, one atom of noble gas is considered to be a molecule of noble gas. This is called a monatomic molecule. Ne represents an atom of Ne and a molecule of Ne.


Diatomic Molecules

Br, I, N, Cl, H, O and F are so reactive that they exist in a more chemically stable state when they covalently bond with another atom of their own element to make two-atom, or diatomic molecules.

Br2, I2, N2, Cl2, H2, O2 and F2

The decomposition of water: 2 H2O 2 H2 + O2

the atom 1) nucleonsnucleons 2) isotopesisotopes 6) electron configuationelectron configuation 7)...

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