atoms,molecules and ion (chemistry university)

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CHM092CHAPTER 1:ATOMS, MOLECULES AND IONS

Siti Fatimah Aminuddin, Pusat Asasi UiTM

Material from karentimberlake.com and H. Stephen Stoker

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ATOMS, MOLECULES AND IONS

1.1 Elements and compounds1.2 Atomic structure; Electrons, protons and neutrons1.3 Atomic number, mass number and isotopes1.4 Chemical formulas1.5 Naming of compounds1.6 Balancing chemical equations


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1.1 ELEMENTS AND COMPOUNDS


Molecular View of Elements and Compounds

4Tro: Chemistry: A Molecular Approach, 2/e


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Classifying Elements & Compounds


• Atomic elements = elements whose particles are single atoms• Molecular elements = elements whose particles

are multi-atom molecules• Molecular compounds = compounds whose

particles are molecules made of only nonmetals• Ionic compounds = compounds whose particles

are cations and anions


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Elements

• Most elements have single atoms as their constituent particles

• The atoms may be physically attracted to each other, but are not chemically bonded together

• A few elements have molecules as their constituent particles

• The molecules are made of two or more atoms chemically bonded together by covalent bonds6

Tro: Chemistry: A Molecular Approach, 2/e


Covalent Bonds

• A chemical bond in which 2 atoms share a single of electron to form one bond.

• Example: H and H• Two nonmetal atoms form a covalent bond because

they have less energy after they bonded.

H + H H : H = HH = H2

hydrogen molecule

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Elements and Compounds

n Elements combine together to make an almost limitless number of compounds

n The properties of the compound are totally different from the constituent elements


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Formation of Water

from Its Elements



Covalent Bonds in H2O

n Other molecules having single covalent bonds, e.g: H2O.

n The hydrogens share their electrons with oxygen so that O has 8 e- and each H has 2 e-.

Ø Show bonding electrons as a single line; show nonbonding electrons as a pair of Lewis dots

Lone pair of electrons (unshared pair)

H O H

Lone pair of electrons (unshared pair)

Molecular Elements

H2

Cl2

Br2

I2

77A

N2 O2 F2


• Certain elements occur as 2 atom moleculesü rule of 7’s

• Other elements occur as polyatomic moleculesü P4, S8, Se8

Molecular Elements



Double Covalent Bond

• 2 pairs of electrons are shared between 2 atoms.• Example: O2

O + O O::O double bond


Triple Covalent Bond

• 3 pairs of electrons are shared between 2 atoms.• Example: N2

N + N N:::N triple bond


Diatomic Elements• Elements that are naturally in molecules with 2

atoms each.• HONClBrIF• Existing as diatomic molecule yields a stable octet• Gases that exist as diatomic molecules are H2, F2,

N2, O2, Cl2, Br2, I2• Examples in naming diatomic molecules:

H2 - hydrogen O2 - oxygen

N2 - nitrogen

Cl2 - chlorine I2 - iodine


Compounds

• Some compounds are composed of ions arranged in a 3-dimensional pattern – these are called ionic compounds– each cation is surrounded by anions, and vice-

versa• Other compounds are composed of individual

molecule units• Each molecule contains atoms of different

elements chemically attached by covalent bonds16


Ionic vs. Molecular Compounds

Propane – contains individual C3H8 molecules

Table salt – containsan array of Na+ ionsand Cl- ions


Ionic Compounds

• Compounds of metals with nonmetals are made of ions

– metal atoms form cations, nonmetal atoms form anions

• No individual molecule units, instead they have a 3-dimensional array of cations and anions made of formula units

• Many contain polyatomic ions– several atoms attached together by covalent

bonds into one ion18Tro: Chemistry: A Molecular Approach, 2/e

Classify Each of the Following as Either an Atomic Element, Molecular Element, Molecular Compound, or Ionic

Compound

Aluminum, AlAluminum chloride, AlCl3Chlorine, Cl2Acetone, C3H6OCarbon monoxide, COCobalt, Co

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atomic element

ionic compound

molecular element

molecular compound

molecular compound

atomic element


1.2 ATOMIC STRUCTURE; ELECTRONS, PROTONS AND NEUTRONS

ATOMIC STRUCTURE


ELECTRON PROTON NEUTRON

Charge -1 +1 0

Occurrence Outside of the nucleus

In the nucleus In the nucleus

Mass (g) 9.109 x 10-28 1.673 x 10-24 1.675 x 10-24

Relative mass 1 1836 1839

+-

1.3 ATOMIC NUMBER, MASS NUMBER AND ISOTOPES

Elements

• Each element has a unique number of protons in its nucleus

• The number of protons in the nucleus of an atom is called the atomic number

– the elements are arranged on the Periodic Table in order of their atomic numbers

• Each element has a unique name and symbol– symbol either one or two letters

• one capital letter or one capital letter and one lowercase letter




The Periodic Table of the Elements

Some symbols come from the element ‘s name, like C for carbon. Others come from the Latin name of the element, like Au for gold (aurum) and Cu for copper (cuprium)

Some symbols are one capital letter, like C, S, and I. Others are two letters, and the second is lowercase, like Br and Sr

The atomic number tells you how many protons are in the nucleus and how many electrons are in the atom

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Structure of the Nucleus

• Soddy discovered that the same element could have atoms with different masses, which he called isotopes– there are two isotopes of chlorine found in

nature, one that has a mass of about 35 amu and the other about 37 amu

• The observed mass is a weighted average of the weights of all the naturally occurring atoms– the percentage of an element that is one

isotope is called the isotope’s natural abundance

– the atomic mass of chlorine is 35.45 amuTro: Chemistry: A Molecular Approach, 2/e

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Isotopes

n All isotopes of an element are chemically identicaln undergo the exact same chemical reactions

n All isotopes of an element have the same number of protons

n Isotopes of an element have different massesn Isotopes of an element have different numbers

of neutronsn Isotopes are identified by their mass numbers,

which is the sum of all the protons and neutrons in the nucleus


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Isotopes• Atomic number

ü Number of protonsü Z

• Mass Numberü Protons + neutronsü whole numberü A

• Abundance = relative amount found in a sample



Example of isotope: Neon

9.25%221210Ne-22 or

0.27%211110Ne-21 or

90.48%201010Ne-20 or

Percent Natural Abundance

A, Mass Number

Number of Neutrons

Number of Protons

Symbol

Ne2010

Ne2110

Ne2210

Practice – Complete the table

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Al2713




Al2713

C136

Mo9642

Cs13355

Example 2.3b: How many protons, electrons, and neutrons are in an atom of ?

for most stable isotopes, n0 ≥ p+Check:

Z = 24 = # p+# e− = # p+ = 24

Solution:

in neutral atom, # p+ = # e-mass number = # p+ + # n0

Conceptual Plan:

Relationships:

therefore A = 52, Z = 24

# p+, # e−, # n0

Given:Find: C

r

5224

symbol atomicnumber

# p+ # e−

symbol

atomic & massnumbers

# n0

A = Z + # n052 = 24 + # n028 = # n0

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Cr

5224


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Reacting Atomsn When elements undergo chemical reactions, the

reacting elements do not turn into other elementsn Statement 4 of Dalton’s Atomic Theory

n This requires that all the atoms present when you start the reaction will still be there after the reaction

n Because the number of protons determines the kind of element, the number of protons in the atom does not change in a chemical reaction

n However, many reactions involve transferring electrons from one atom to another


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Charged Atoms

n When atoms gain or lose electrons, they acquire a charge

n Charged atoms or groups of atoms are called ions

n When atoms gain electrons, they become negatively charged ions, called anions

n When atoms lose electrons, they become positively charged ions, called cations


Ions and Compounds

• Ions behave much differently than the neutral atoms

– e.g., the metal sodium, made of neutral Na atoms, is highly reactive and quite unstable; however, the sodium cations, Na+, found in table salt are very nonreactive and stable

• Because materials such as table salt are neutral, there must be equal amounts of charge from cations and anions in them


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Atomic Structures of Ions

• Nonmetals form anions• For each negative charge, the ion has

one more electron than the neutral atom– F = 9 p+ and 9 e−, F− = 9 p+ and 10 e−– P = 15 p+ and 15 e−, P3− = 15 p+ and 18

e−• Anions are named by changing the

ending of the name to -idefluorine F + 1e− F− fluoride ionoxygen O + 2e− O2− oxide ionTro: Chemistry: A Molecular Approach, 2/e


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Ion Charge and the Periodic Table

n The charge on an ion can often be determined from an element’s position on the Periodic Table

n Metals always form positively charged cationsn For many main group metals, the charge = the

group numbern Nonmetals form negatively charged anionsn For nonmetals, the charge = the group

number − 8



Practice – What is the charge on each of the following ions?

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• potassium cation• sulfide anion• calcium cation• bromide anion• aluminum cation

K+S2−Ca2+Br−Al3+




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+3Al




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+2Mg

−2S

−Br

+3Al


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Example 2.5: If copper is 69.17% Cu-63 with a mass of 62.9396 amu and the rest Cu-65 with a mass of 64.9278

amu, find the atomic mass of copper

the average is between the two masses, closer to the major isotope

Check:

Solution:

Conceptual Plan:Relationships:

Cu-63 = 69.17%, 62.9396 amuCu-65 = 100-69.17%, 64.9278 amuatomic mass, amu

Given:

Find:

isotope masses,isotope fractions

avg. atomic mass


Practice Problem

There are two isotopes of Gallium: Ga-69 with mass 68.9256 amu and abundance of 60.11%; and Ga-71 with mass 70.9247 amu and

abundance of 39.89%.

Calculate the atomic mass of gallium.


Practice – Ga-69 with mass 68.9256 amu and abundance of 60.11% and Ga-71 with mass 70.9247 amu and abundance of

39.89%. Calculate the atomic mass of gallium.

the average is between the two masses, closer to the major isotope

Check:

Solution:

Conceptual Plan:Relationships:

Ga-69 = 60.11%, 68.9256 amuGa-71 = 39.89%, 70.9247 amuatomic mass, amu

Given:

Find:

isotope masses,isotope fractions

avg. atomic mass


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atoms,molecules and ion (chemistry university)