atoms, molecules and ions atoms, molecules and ions

Atoms, Atoms, Molecules Molecules and Ionsand Ions

One of the main challenges of chemistry is to understand the connection between the

macroscopic world that we experience and the microscopic world of atoms and

molecules.

- You must learn to think on the atomic level -

Scanning Tunneling Microscope (STM)Scanning Tunneling Microscope (STM)

– a special microscope used to "see" individual atoms.

– it uses an electron from a tiny needle to probe the surface of the substance.

Dalton's Atomic TheoryDalton's Atomic Theory

• Each element is made up of tiny particles called atoms.

• The atoms of a given element are identical; the atoms of different elements are different in some fundamental way or ways.

• Chemical compounds are formed when atoms of different elements combine w/each other. A given compound always has the same relative numbers and types of atoms.

• Chemical reactions involve reorganization of the atoms --changes in the way they are bound together. The atoms themselves are not changed in a chemical reaction.

The Structure of the AtomThe Structure of the Atom

Atoms

- are really small

- are shaped like a sphere but is mostly empty inside.

- at it's center is a space called the nucleus that contains 2 types of particles

1. proton

2. neutron

- electron are spread around the nucleus

The nucleus is:

Small compared with the overall size of the atom.

Extremely dense; accounts for almost all of the atom’s mass.

Nuclear Atom Viewed in Cross Section

Neutrons – found in the nucleus;

no charge;

virtually same mass as a proton.

Protons – found in the nucleus;

positive charge equal in magnitude to the electron’s negative charge.

Electrons –

found outside the nucleus;

negatively charged.

> # of protons = # of electrons

* atoms are electrically neutral

>Atomic number = # of protons

- Defines an element because the atoms of a particular element have a specific number of protons .

> Mass number = protons+ neutrons

N14

7

Nitrogen Atom

Two Isotopes of SodiumIsotopes- - Atoms with the same number of protons but different Atoms with the same number of protons but different numbers of neutronsnumbers of neutrons.

- The elements are arranged by atomic number (the number above the element symbol) in horizontal rows called periods and in vertical columns known as groups or families, according to similarities in their chemical properties.

- The periodic table was proposed by the Russian chemist Dimitri Mendeleev

The Periodic TableThe Periodic Table

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Special Names for Groups in the Periodic Table

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Metals Versus Nonmetals

Molecules Molecules

- formed when atoms react by sharing electrons forming covalent bonds.

- most are composed of nonmetallic elements.

> a molecule may contain atoms of the same element or atoms of 2 or more elements joined in a fixed ratio.

* If the atoms belong to different elements , then the molecule is also known as a covalent compound.

An ion is an atom or group of atoms that has a net positive or negative charge (because they have either lost or gained electron)

> cations - positive; atoms that lose electrons ; in most cases are derived from metals

> anions - negative; atoms that gain electrons; in most cases are derived from nonmetals

> Because anions & cations have opposite charges , they attract each other forming ionic compounds. This force of attraction between oppositely charged ions is called ionic bonding.

Ions Ions

- can be represented in several different ways. The simplest method is the chemical formula, in w/c the symbols for the elements are used to indicate the types of atoms present & subscripts are used to indicate the relative number of atoms.

e.g.

CO2 => contains 1 atom of carbon & 2 atoms of oxygen

Covalent & Ionic Compounds

Binary Ionic Compounds Metal—nonmetal

Naming Compounds Naming Compounds

Binary Compounds Composed of two

elements Ionic and covalent

compounds included

Binary Covalent Compounds Nonmetal—nonmetal

> Review & familiarize yourself w/the names of the elements on the Periodic Table & their corrresponding

symbols <

Flowchart for Naming Binary Compounds (Fig. 3.10)

1. The cation is always named first and the anion second.

2. A monatomic cation takes its name from the name of the parent element.

3. A monatomic anion is named by taking the root of the element name and adding –ide.

Binary Ionic Compounds (Type I)

Examples:

KCl Potassium chloride

MgBr2 Magnesium bromide

CaO Calcium oxide

• Metals in these compounds form more than one type of positive charge.

• Charge on the metal ion must be specified.• Roman numeral indicates the charge of the metal

cation.• Transition metal cations usually require a

Roman numeral.

Binary Ionic Compounds (Type II)

Examples:

CuBr Copper(I) bromide

FeS Iron(II) sulfide

PbO2 Lead(IV) oxide

• Review & familiarize yourself w/the Common Polyatomic Ions (see Table 3.5)

• Examples of compounds containing polyatomic ions:

NaOH Sodium hydroxide

Mg(NO3)2 Magnesium nitrate

(NH4)2SO4 Ammonium sulfate

Polyatomic Ions

Prefixes Used to Indicate Number in Chemical Names

• Formed between two nonmetals.

1. The first element in the formula is named first, using the full element name.

2. The second element is named as if it were an anion.

*A monatomic anion is named by taking the root of the element name and adding –ide.*

3. Prefixes are used to denote the numbers of atoms present.

4. The prefix mono- is never used for naming the first element.

Binary Covalent Compounds (Type III)

Examples:

CO2 Carbon dioxide

SF6 Sulfur hexafluoride

N2O4 Dinitrogen tetroxide

• Acids can be recognized by the hydrogen that appears first in the formula—HCl.

• Molecule with one or more H+ ions attached to an anion.

Acids

Flowchart for Naming Acids

• If the anion does not contain oxygen, the acid is named with the prefix hydro– and the suffix –ic.

• Examples:

HCl Hydrochloric acid

HCN Hydrocyanic acid

H2S Hydrosulfuric acid

Acids

• If the anion does contain oxygen: The suffix –ic is added to the root name if

the anion name ends in –ate.• Examples:

HNO3Nitric acid

H2SO4 Sulfuric acid

HC2H3O2 Acetic acid

Acids

• If the anion does contain oxygen: The suffix –ous is added to the root name if

the anion name ends in –ite.• Examples:

HNO2Nitrous acid

H2SO3 Sulfurous acid

HClO2 Chlorous acid

Acids