Add metal hydride naming

Chapter 2Atoms, Molecules,

and Ions

Atomic Theory of Matter

The theory that atoms are the fundamental building blocks of matter reemerged in the early 19th century, championed by John Dalton.

Dalton’s Postulates

1. Each element is composed of extremely small particles called atoms.

Dalton’s Postulates

2. All atoms of a given element are identical to one another in mass and other properties, but the atoms of one element are different from the atoms of all other elements.

* He was a little wrong on this one…isotopes!

Dalton’s Postulates

3. Atoms of an element are not changed into atoms of a different element by chemical reactions; atoms are neither created nor destroyed in chemical reactions.

Law of Conservation of Mass

Dalton’s Postulates

4. Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms.

Law of Definite Proportions(a.k.a. Law of Constant Composition)See Chapter 1 Notes

Dalton also deduced theLaw of Multiple Proportions

CO2 CO

2.671.33

=2.00 *This is always a whole number!

The Electron• J. J. Thompson is credited with their

discovery (1897).• Streams of negatively charged particles were

found to emanate from cathode tubes.

Millikan Oil Drop Experiment

Determined the charge & mass of the electron

Discovery of the Nucleus

Ernest Rutherford shot particles at a thin sheet of gold foil and observed the pattern of scatter of the particles.

The Nuclear Atom

• Rutherford postulated a very small, dense nucleus with the electrons around the outside of the atom.

• Most of the volume of the atom is empty space.

Other Subatomic Particles

• Protons were discovered by Rutherford in 1919.

• Neutrons were discovered by James Chadwick in 1932.

Subatomic Particles

(The mass of an electron is so small we ignore it.)

Symbols of Elements

Elements are symbolized by one or two letters.

Atomic Number

All atoms of the same element have the same number of protons

Mass Number

The mass number is the total number of protons and neutrons in the atom.

Isotopes:

• Atoms of the same element with different masses.

• Isotopes have different numbers of neutrons.116C 12

6C13

6C14

6C

Atomic Mass (Weight) of an Atom

The actual mass can be calculated for any atom:• Actual Mass (g) = (Mass#)(1.67x10-24g)

• This can be converted to an atomic mass by relating the mass to carbon-12

Mass of one atom in amu = Mass of a mole of atoms in grams!

*Scientists defined the mole so this would work!

Atomic Mass (Weight) of an Element

• A weighted average of atomic masses of all the isotopes of an element.

Use the following data to calculate the atomic mass for the element Magnesium

Isotope Atomic Mass of Isotope Abundance

Mg - 24 23.982628 µ 78.600 %Mg - 25 24.963745 µ 10.11 %Mg - 26 25.960802 µ 11.29 %

(.78600) (23.982628 g) + (.1011) (24.963745 g) + (.1129) (25.960802

g)

18.850 g + 2.524 g + 2.931 g 24.305 g/mol

Add mass spec here(see end of ppt)

Periodic Table:

• A systematic catalog of elements.

• Elements are arranged in order of atomic number.

Periodic Table

• The rows on the periodic chart are periods.

• Columns are groups.• Elements in the same

group have similar chemical properties.

Groups

These five groups are known by their names.

Periodic Table

Nonmetals are on the right side of the periodic table (with the exception of H).

Periodic Table

Metalloids border the stair-step line (with the exception of Al and Po).

Periodic Table

Metals are on the left side of the chart.

Chemical FormulasThe subscript to the right of the symbol of an element tells the number of atoms of that element in one molecule of the compound.

Types of Formulas• Empirical formulas give the lowest

whole-number ratio of atoms of each element in a compound.

• Molecular formulas give the exact number of atoms of each element in a compound.

• Molecular Formula: C6H12O6

• Empirical Formula: CH2O

Ions

• When atoms lose or gain electrons, they become ions.Cations are positive Anions are negative

Ionic BondsIonic compounds (such as NaCl) are generally formed between metals and nonmetals.

*See handout on naming and writing formulas!

Molecular CompoundsMolecular compounds are composed of molecules and almost always contain only nonmetals.

*See handout on naming and writing formulas!

Diatomic Molecules

These seven elements occur naturally as molecules containing two atoms.

HONClBrIF

Acids

• Compounds containing hydrogen with something that looks like a negative ion

(for now at least…..)

*See handout on naming and writing formulas!

Organic Molecules (Alkanes)

• Organic molecules contain carbon.

• Alkanes are the most simple organic compounds. They have chains of carbon with only single bonds surrounded by hydrogen.

• They are named by the number of carbons in the chain + the suffix -ane

Alkanes# of carbons Name of alkane

1 Methane

2 Ethane

3 Propane

4 Butane

5 Pentane

6 Hexane

7 Heptane

8 Octane

9 Nonane

10 Decane

Alcohol• Other classifications of organic

compounds have multiple bonds or other atoms or groups of atoms replacing a hydrogen.

• Alcohol has an –OH group instead of a –H off one of the carbons in an alkane

• They are named with the same root as the alkanes + the suffix -ol Starting with propanol they include a

number in front of the name indicating which carbon the –OH is bonded to

Mass Spectroscopy

Atomic Mass (Weight) of an Element

• A weighted average of atomic masses of all the isotopes of an element.

Use the following data to calculate the atomic mass for the element Magnesium

Isotope Atomic Mass of Isotope Abundance

Mg - 24 23.982628 µ 78.600 %Mg - 25 24.963745 µ 10.11 %Mg - 26 25.960802 µ 11.29 %

(.78600) (23.982628 g) + (.1011) (24.963745 g) + (.1129) (25.960802

g)

18.850 g + 2.524 g + 2.931 g 24.305 g/mol

Where does that data come from?

• Mass SpectroscopyAtoms that go into the mass spectrometer

are organized by mass and the relative amounts are measured.

This is how we found isotopes and disproved part (the only part so far) of Dalton’s Atomic Theory.

Mass Spec for Molybdenium

- we will assume the charge is +1…so this is the atomic mass

http://www.chemguide.co.uk/analysis/masspec/howitworks.html#top

Estimating Atomic Mass of an Element from its Mass Spectrum

This scale is usually made by setting the tallest line at 100

100

23

All we really care about is this ratio…if we have 123 atoms, 23 would be B-10 and 100 would be B-11

• You can either find the % abundance

and proceed as you learned 1st year.

Or just use the ratios as they are…

)

( 23123 ) (10 )+( 100123 )(11 )=10.9