Chapter 2 · 2017. 11. 13. · Ions Formation of Monatomic Ions cation (positively charged), anion...

Chapter 2

Atoms, Molecules, and Ions

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Atomic theory : on the basis of Dalton’s theory

Components : proton, neutron, electron

Atomic Number : number of protons

Mass Number : number of protons and neutrons

Nuclear Stability : radioactivity

Atomic Theory

Postulates

Elements consist of tiny particles called atoms which retain their identity in reactions

In a compound, atoms of two or more elements are combined in a fixed ratio of small whole numbers; e. g. 1:1, 2:1, etc.

Some features of Dalton’s theory

Cathode ray tube

Rutherford’s scattering experiment

Components

Atomic Number

Atomic number

equals number of protons in nucleus

equals number of electrons in neutral atom

is a characteristic of a particular elementall H atoms have 1 proton, all He atoms have 2 protons, etc.

Mass Number

Mass numberequals number of protons + number of neutronsatoms of the same element can differ in mass number

atomic nuclear massprotons neutrons number symbol number

carbon-12 6 6 6 12

carbon-14 6 8 6 14

Nuclear Stability

Neutron-to-proton ratio increases with atomic number.

Unstable isotopes decompose by radioactivity. Ordinarily the result is the transmutation of elements

Nuclear Stability - Belt of stability

Periodic table

Structure : period (horizontal rows) & group (vertical columns)

Metals, Nonmetals, & Metalloids

metal : high electrical conductivity

metalloid : intermediate electrical conductivity between

metal and nonmetal

Structure

Periods : horizontal rows

Groups : vertical columnsnumbering system for groups

Metals, Nonmetals, Metalloids

MetalsAbout 80 elementslocated at lower left of periodic table

NonmetalsAbout 18 elementslocated at upper right of periodic table

Metalloids

B, Si, Ge, As, Sb, Te

Molecules

Composition : isolated atoms and combined atomes

Types of Formulasmolecular : number of atoms of each element is indicated by a

subscript written after the symbol of the elementstructural : bonding pattern within the moleculecondensed structural : bonding pattern in the molecule and

highlights the presence of a reactive group

Composition

Two or more atoms may combine with one another to form an uncharged molecule. Usually nonmetal atoms made up molecules.

Within the molecule, atoms are held together by covalent bonds

Types of Formulas

Consider the molecule ethaneMolecular formula: C2H6

Structural formula:

Condensed structural formula: CH3CH3 ( -CH3 is alkyl)

Molecular elements and their physical states

Formation of Monatomic Ions

cation (positively charged), anion (negatively charged)

Charges of Monatomic Ions with noble-gas structure

atoms form ions that contain the same number of

electrons as the neighboring noble-gas atom

Polyatomic Ions

Formulas of compoundsthe total positive charge of the cations in the formula must equal the total negative charge of the anions

Formation of Monatomic Ions

Formation

Cation : Na atom (11p+, 11e -) → Na+ ion (11p+, 11e -) + e -

Anion : F atom (9p+, 9e -) + e - → F - ion (9p+, 10e -)

Charges of Monatomic Ions with noble-gas structures

Cation: Group 1 (+1); Group 2 (+2); Al3+

Anion: Group 16 (-2); Group 17 (-1); N3-

Formulas of compounds

Apply principle of electroneutralitycalcium fluoride: Ca2+, F- ions: CaF2

aluminum nitrate: Al3+, NO3- : Al(NO3)3

sodium dihydrogen phosphate: Na+, H2PO4- : NaH2PO4

Names of Compounds

Ionic : consist of two words – first names the cation and the

second names the anion

Binary Molecular Compounds : when two nonmetals combine

with each other, the product is most often a binary

molecular compounds

Acids : form H+ ions

Name cation followed by anion

Note that with transition metal cations, charge is indicated by Roman numeralNa2SO4 sodium sulfateFe(NO3)3 iron (III) nitrate

Ionic (cont.)

Systematic names of oxoanions-ate, -ite, per-, hypo--per (largest number of oxygen atoms) > -ate > -ite > -hypeCalcium hypochlorite: Ca(ClO)2

Binary Molecular Compounds

The first word gives the name of the element that appears first in the formula and the second. Greek prefixes are used to show the number of atoms of that element in the formula

SF6 sulfur hexafluorideN2O3 dinitrogen trioxide

Binary Acids: containing H atoms ionize in water to form H+ ionshydrochloric acid (HCl)

Oxoacids: simply related to those of the corresponding oxoanionsate salt → ic acidite salt → ous acid

Examples:HClO4 perchloric acidHClO hypochlorous acid

Chapter 2 · 2017. 11. 13. · Ions Formation of Monatomic Ions cation (positively charged), anion...

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