ch # 5 atoms, molecule, formulas, subatomic particles

Ch # 5Ch # 5

Atoms, Molecule, Formulas, Atoms, Molecule, Formulas, Subatomic Particles.Subatomic Particles.

AtomsAtoms

An atom is the smallest An atom is the smallest particle of an element that particle of an element that can exist and still have can exist and still have properties of the element.properties of the element.

Atomic Theory of MatterAtomic Theory of Matter

All matter is made up of small particles All matter is made up of small particles called atoms.113 types.called atoms.113 types.

Atoms of same element are similar to Atoms of same element are similar to one another.one another.

The relative number and arrangement The relative number and arrangement of different types of atoms contained in of different types of atoms contained in a pure substance determined its a pure substance determined its identity.identity.

Atomic Theory of Atoms.Atomic Theory of Atoms.

These atoms rearrange, These atoms rearrange, separate or unite to form a new separate or unite to form a new substance.substance.

Atoms can participate in or result Atoms can participate in or result from any chemical change, from any chemical change, atoms cannot be destructed.atoms cannot be destructed.

An atom is very SmallAn atom is very Small

The diameter of an atom The diameter of an atom is 0.1 to 0.5 nm.is 0.1 to 0.5 nm.

This is 1 to 5 ten billionths of a meter.

If the diameter of this dot is 1 mm, then 10 million hydrogen atoms would form a line across the dot.

The MoleculeThe Molecule

A group of two or more atoms A group of two or more atoms that is strongly bound to each that is strongly bound to each other. other.

The MoleculeThe Molecule Diatomic moleculeDiatomic molecule: contains 2 : contains 2

atoms.H,N,O,F,Cl,Br,I, atoms.H,N,O,F,Cl,Br,I, Triatomic moleculeTriatomic molecule: Contains 3 atoms.: Contains 3 atoms. P-4 atoms, S-8 atoms.P-4 atoms, S-8 atoms. Homoatomic moleculeHomoatomic molecule: All atoms are of : All atoms are of

same kind.same kind. Heteroatomic moleculeHeteroatomic molecule: Two or more : Two or more

different kinds of atoms are present.different kinds of atoms are present.

Molecular compoundsMolecular compounds

Compounds that have heteroatomic Compounds that have heteroatomic molecule as basic structural unit.molecule as basic structural unit.

Ex: table sugar-sucrose.Ex: table sugar-sucrose. Molecule is a limit of physical sub-Molecule is a limit of physical sub-

division. Atom is a limit of chemical division. Atom is a limit of chemical sub-division. sub-division.

Molecular CompoundsMolecular Compounds

Two kinds of atoms present, but, one Two kinds of atoms present, but, one kind of molecule.kind of molecule.

Molecules have different properties than Molecules have different properties than that of the atom.that of the atom.

Ionic compoundsIonic compounds

Compounds that contain ions. Ex: Compounds that contain ions. Ex: NaCl NaCl

Natural and Synthetic Natural and Synthetic compoundscompounds

The compounds could be The compounds could be naturally or artificially made.naturally or artificially made.

Chemical FormulasChemical Formulas

Made up of symbols. Made up of symbols. The subscripts indicate the The subscripts indicate the

number of atoms.number of atoms.Read the formula CRead the formula C66HH1212OO66

ProtonsProtons

• Eugen Goldstein, a German physicist, first observed protons in 1886:

Thompson determined the proton’s Thompson determined the proton’s characteristics.characteristics.

Thompson showed that atoms Thompson showed that atoms contained both positive and negative contained both positive and negative charges.charges.

This disproved the Dalton model of the This disproved the Dalton model of the atom which held that atoms were atom which held that atoms were indivisible.indivisible.

Subatomic Particles.Subatomic Particles.

ProtonsProtons: +ve charge.-Goldstein. Charge: : +ve charge.-Goldstein. Charge: +1+1

ElectronElectron:-ve charge.- Thomson. Smallest :-ve charge.- Thomson. Smallest mass.Charge:-1mass.Charge:-1

NeutronNeutron: No charge.-Chadwick.: No charge.-Chadwick. Opposite charges attract, like charges Opposite charges attract, like charges

repel.repel.

NucleusNucleus: :

Small, dense, positively charged center Small, dense, positively charged center of an atom. It contains protons and of an atom. It contains protons and neutrons. An atoms entire mass is neutrons. An atoms entire mass is concentrated to the center. concentrated to the center.

NucleonNucleon

Any subatomic particle found in the Any subatomic particle found in the nucleus of an atom. Ex; protons and nucleus of an atom. Ex; protons and neutrons.neutrons.

Electrons revolve around the nucleus in a Electrons revolve around the nucleus in a very large region. It is mostly empty very large region. It is mostly empty space.space.

Volume occupied by electrons is called Volume occupied by electrons is called electron cloud. It is negatively charged.electron cloud. It is negatively charged.

An atom as a whole is An atom as a whole is neutral. Number of neutral. Number of protons=Number of protons=Number of electrons in any atom. The electrons in any atom. The +ve and-ve charges cancel +ve and-ve charges cancel each other out.each other out.

Diameter of nucleus= 10-15 Diameter of nucleus= 10-15 m. Entire mass is m. Entire mass is concentrated in the center concentrated in the center of the atom. of the atom.

Protons and neutrons are Protons and neutrons are made of Leptons, Mesons, made of Leptons, Mesons, Baryons.Baryons.

5.6

Atomic Numbers of the Atomic Numbers of the ElementsElementsAtomic Numbers of the Atomic Numbers of the ElementsElements

• The atomic number of an element is equal to the number of protons in the nucleus of that element.

The atomic number of an atom The atomic number of an atom determines which element the atom is.determines which element the atom is.

Every atom with an Every atom with an atomic number of atomic number of 11 is a is a hydrogenhydrogen atom. atom.

Every Every hydrogenhydrogen atom contains atom contains 11 proton in its proton in its nucleus.nucleus.

6 protons in the nucleus 6C

atomic number

Every atom with an atomic number of 6 is a carbon atom.

1 proton in the nucleus

atomic number

Every atom with an atomic number of 1 is a hydrogen atom.

1H

Isotopic Notation

Isotopes of the Isotopes of the ElementsElementsIsotopes of the Isotopes of the ElementsElements

• Atoms of the same element can have different masses.

They always have the same number of They always have the same number of protons, but they can have different protons, but they can have different numbers of neutrons in their nuclei.numbers of neutrons in their nuclei.

The difference in the number of neutrons The difference in the number of neutrons accounts for the difference in mass.accounts for the difference in mass.

These are These are isotopesisotopes of the same element. of the same element.

Isotopes of the Same Isotopes of the Same Element HaveElement Have

Equal numbers of protonsEqual numbers of protons

Different numbers of Different numbers of neutronsneutrons

Hydrogen has three isotopes

1 proton

0 neutrons

1 proton

1 neutron

1 proton

2 neutrons

Examples of Isotopes Examples of Isotopes ElementElementProtonsProtons ElectronsElectrons NeutronsNeutrons SymbolSymbol

HydrogenHydrogen 1 1 11 00 1111HH

HydrogenHydrogen 1 1 11 11 1122H H

HydrogenHydrogen 1 1 11 22 1133HH

UraniumUranium 9292 9292 143 143

9292235235UU

UraniumUranium 9292 9292 146 146

9292238238UU

ChlorineChlorine 17 17 1717 1818

17173535ClCl

ChlorineChlorine 17 17 1717 2020

17173737ClCl

11H21 H

235 92 U

31H

238 92 U

35 17Cl 37 17Cl

Atomic MassAtomic MassAtomic MassAtomic Mass

• The mass of a single atom is too small to measure on a balance.

Using a mass spectrometer, the mass Using a mass spectrometer, the mass of the hydrogen atom was determined. of the hydrogen atom was determined.

Using a mass spectrometer, the mass Using a mass spectrometer, the mass of one hydrogen atom was determined of one hydrogen atom was determined to be 1.673 x 10to be 1.673 x 10--2424 g. g.

smallsmallsmallsmallsmallsmallsmallsmallsmallsmallsmallsmallsmallsmallsmallsmallsmallsmallsmallsmallsmallsmallsmallsmallsmallsmallsmallsmallsmallsmall

smallsmallsmallsmall

smallsmallsmallsmall

smallsmall

This number is very small.

A Modern Mass Spectrometer

A mass spectrogram is recorded.

From the intensity and positions of the lines on the mass spectrogram, the different isotopes and their relative amounts can be determined.

Positive ions formed from sample. Electrical field

at slits accelerates positive ions.

Deflection of positive ions occurs at magnetic field.

5.8

126C

The standard to which the masses of all other atoms are compared to was chosen to be the most abundant isotope of carbon.

1 amu is defined as exactly equal to 1 amu is defined as exactly equal to the mass of a carbon-12 atom the mass of a carbon-12 atom12

1

126C

1 amu = 1.6606 x 10-24 g

HAverage atomic mass 1.00797 amu.Average atomic mass 1.00797 amu.

UAverage atomic mass 248.029 amu.Average atomic mass 248.029 amu.

Average RelativeAverage RelativeAtomic MassAtomic MassAverage RelativeAverage RelativeAtomic MassAtomic Mass

• Most elements occur as mixtures of isotopes.

Isotopes of the same element have Isotopes of the same element have different masses.different masses.

The listed atomic mass of an element is The listed atomic mass of an element is the average relative mass of the isotopes the average relative mass of the isotopes of that element compared to the mass of of that element compared to the mass of carbon-12 (exactly 12.0000…amu).carbon-12 (exactly 12.0000…amu).

Relationship Between Relationship Between Mass Number and Mass Number and Atomic NumberAtomic Number

Relationship Between Relationship Between Mass Number and Mass Number and Atomic NumberAtomic Number

The mass number minus the atomic number equals the number of neutrons in the nucleus.

47109 Ag

mass numberatomic number

number of neutrons

- =

62109 - 47 =

mass number

atomic number

Rutherford’s alpha particle scattering experiment.

5.5