Week 3: Atoms and Elements

atom

is the smallest identifiable unit of an element

Modern Atomic Theory

The theory that all matter is composed of atoms grew out of observations and laws

1. the law of conservation of mass

2. the law of definite proportions

3. the law of multiple proportions

What are the three most important laws that led to the development and acceptance of the atomic theory were….

Antoine Lavoisier

formulated the law of conservation of mass

Created nor Destroyed

In a chemical reaction, matter is neither _____________

Law of conservation of mass

The total mass of the substances involved in the reaction does not change

Law of conservation of mass

The law is consistent with the idea that matter is composed of small, indestructible particles.

A

When a log completely burns in a campfire, the mass of the ash is much less than the mass of the log. What happens to the matter that composed the log?

a. The matter that composed the log reacts to form gases that are released into the air.

b. The matter that composed the log is converted into energy.

c. The matter that composed the log is still present in the ashes but has a much lower mass.

Joseph Proust, 1797

formulated the law of definite proportions

Law of Definite Proportions

All samples of a given compound, regardless of their source or how they were prepared, have the same proportions of their constituent elements.

Law of Definite Proportions

All samples of a given compound, regardless of their source or how they were prepared, have the same proportions of their constituent elements.

d

We just saw that the mass ratio of nitrogen to hydrogen in ammonia is 4.7:1. If a sample of ammonia contains 10.0 grams of H, how many grams of N does it contain?

a. 4.7

b. 9.4

c. 14

d. 47

John Dalton, 1804

published his law of multiple proportions

Law of multiple proportions

When two elements A and B form two different compounds, the masses of B that combine with a fixed mass of A can be expressed in small whole number ratios.

A

Which statement best captures one of the differences between the law of definite proportions and the law of multiple p proportions?

a) The law of definite proportions applies to two or more samples of the same compound, while the law of multiple proportions applies to two different compounds containing the same two elements (A and B).

b) The law of definite proportions applies to two different compounds containing the same two elements (A and B), while the law of multiple proportions applies to two or more samples of the same compound.

c) None of the above. Both laws apply to multiple samples of the same

compound.

1. Each element is composed of tiny, indestructible particles called atoms.

2. All atoms of a given element have the same mass and other properties that distinguish them from the atoms of other elements.

3. Atoms combine in simple, whole-number ratios to form compounds.

4. Atoms of one element cannot change into atoms of another element.

Dalton’s atomic theory explained the laws as follows

atoms

Every sample of an elements is made of many _____

Atoms

The smallest particle of an element

Nucleus and a cloud of electrons

Atoms are made of 2 parts

Nucleus

the hard center of an atom Contains protons and neutrons

Electron

Outside the nucleus

1.00727

What is the mass of proton(amu)

1.00866

What is the mass of neutron(amu)

0.00055

What is the mass of electron(amu)

Isotopes

Atoms with the same number of protons but a different number of neutrons are called

Ions

Atoms can lose or gain electrons during chemical change and become charged particles called

cations

Positively charged ions, such as Na+, are called

anions

Negatively charged ions, such as F−, are called

B

In light of the nuclear model of the atom, which statement is true?

a. For a given element, the size of an isotope with more neutrons is larger than one with fewer neutrons.

b. For a given element, the size of an atom is the same for all of the element’s isotopes.

Mendeleev, 1869

noticed that certain groups of elements had similar properties

Mendeleev, 1869

He found that when elements are listed in order of increasing mass, these similar properties recurred in a periodic pattern.

To be periodic

means to exhibit a repeating pattern.

Clemens Winkler, 1886

eka-silicon was discovered by ___________, who named it germanium

• Good conductors of heat and electricity

• Can be pounded into flat sheets (malleability)

• Can be drawn into wires (ductility)

• Often shiny

• Tend to lose electrons when they undergo chemical changes

properties of metals

Properties of nonmetals

• Poor conductors of heat and electricity

• Not ductile and not malleable

• Gain electrons when they undergo chemical changes

Metalloids

are sometimes called semimetals

Main group elements

whose properties tend to be largely predictable based on their position in the periodic table

Transition elements or transition metals

whose properties tend to be less predictable based simply on their position in the periodic table

Noble gases

The group 8A elements, called the ________, are mostly unreactive

alkali metals

The group 1A elements, called the ________, are all reactive metals

alkaline earth metals

The group 2A elements are called the _________

halogens

The group 7A elements, the __________, are very reactive nonmetals.

isoelectronic

• A main-group metal tends to lose electrons, forming a cation with the same number of electrons (________) as the nearest noble gas

• A main-group nonmetal tends to gain electrons, forming an anion with the same number of electrons (___________) as the nearest noble gas

to lose one electron and form +1 ions

In general, the alkali metals have a tendency

to lose two electrons and form +2 ions

The alkaline earth metals (group 2A) tend

to gain one electron and form −1 ions

The halogens (group 7A) tend

to gain two electrons and form −2 ions

The oxygen family nonmetals (group 6A) tend

Atomic mass

is sometimes called atomic weight or standard atomic weight