Atoms and Elements

Chemical FoundationsChemical Foundations

Atoms and ElementsAtoms and Elements

Element - Substances that can not be broken down further by ordinary chemical means

Atoms - The smallest particle of an element that retains the properties of the element

Element - Substances that can not be broken down further by ordinary chemical means

Atoms - The smallest particle of an element that retains the properties of the element

PostulatesPostulates

Elements consist of tiny particles called atoms

Atoms retain their identity in reactions They do not change into other types of

atoms Carbon stays carbon, Oxygen stays oxygen

In a compound, atoms of two or more elements are combined

Elements consist of tiny particles called atoms

Atoms retain their identity in reactions They do not change into other types of

atoms Carbon stays carbon, Oxygen stays oxygen

In a compound, atoms of two or more elements are combined

Atoms have partsAtoms have parts

Atoms are composed of protons, neutrons and electrons

All of the parts of the atom stay together as that atom in chemical reactions

Atoms are composed of protons, neutrons and electrons

All of the parts of the atom stay together as that atom in chemical reactions

ElementsElements

Elements represent the different types of atoms that are known

Come in solid, liquid and gas forms at earths normal temperatures

Elements represent the different types of atoms that are known

Come in solid, liquid and gas forms at earths normal temperatures

Top Ten Top Ten

Most Abundant Elements on Earth

Most Abundant Elements on Earth

Most Common ElementsMost Common Elements

A collection of argon atoms.

A collection of argon atoms.

Diatomic ElementsDiatomic Elements

Nitrogen gas contains N2 molecules.Nitrogen gas contains N2 molecules.

Oxygen gas contains O2 molecules. Oxygen gas contains O2 molecules.

Representation of NO, NO2, and N2O.

Representation of NO, NO2, and N2O.

History of the discovery of the atom

History of the discovery of the atom

300 BC in Greece School of thought that matter is made

up of tiny indivisible, invisible, indestructable, fundamental units of matter called atmos

Democritus of Abdera most well known atmostist. Did no experiments No proof philosopher

300 BC in Greece School of thought that matter is made

up of tiny indivisible, invisible, indestructable, fundamental units of matter called atmos

Democritus of Abdera most well known atmostist. Did no experiments No proof philosopher

1770’s1770’s

Antoine Lavosier made observations and did experiments resulting in the Law of Conservation of Mass

Law of Conservation of Mass Matter can not be created or destroyed Mass of materials before the chemical

reaction is the same mass after the reaction

Antoine Lavosier made observations and did experiments resulting in the Law of Conservation of Mass

Law of Conservation of Mass Matter can not be created or destroyed Mass of materials before the chemical

reaction is the same mass after the reaction

1799 - Proust1799 - Proust

Joseph Proust showed that the proportion by mass of the elements in a compound is always the same

Now called the Law of Definite Proportions

Part of our definition of a chemical - any substance with a definite composition

Joseph Proust showed that the proportion by mass of the elements in a compound is always the same

Now called the Law of Definite Proportions

Part of our definition of a chemical - any substance with a definite composition

John DaltonJohn Dalton

English School Teacher Alchemists were trying to change different

metals into gold Wanted to learn in what ratios that

different elements combine Performed experiments Formulated theories to explain his

observations Proposed his theories in 1808 Based on the Greek idea of the atom

English School Teacher Alchemists were trying to change different

metals into gold Wanted to learn in what ratios that

different elements combine Performed experiments Formulated theories to explain his

observations Proposed his theories in 1808 Based on the Greek idea of the atom

Key idea - Dalton’s Atomic Theory

Key idea - Dalton’s Atomic Theory

All matter is made of indivisible, invisible, and indestructible particles called atoms

Atoms of the same element are identical

Atoms of different elements differ in their physical and chemical properties

All matter is made of indivisible, invisible, and indestructible particles called atoms

Atoms of the same element are identical

Atoms of different elements differ in their physical and chemical properties

Dalton’s Atomic Theory Con’t

Dalton’s Atomic Theory Con’t

Atoms of different elements combine in simple whole number ratios to form compounds

Chemical Reactions occur when atoms are separated, joined or rearranged. Atoms of one element are NEVER changed into atoms of another element as a result of a reaction

Atoms of different elements combine in simple whole number ratios to form compounds

Chemical Reactions occur when atoms are separated, joined or rearranged. Atoms of one element are NEVER changed into atoms of another element as a result of a reaction

1870’s1870’s

William Crooks developed the Crook’s Tube A tube with sealed gases and metal

plates at the end Run a current through the metal, and

a glowing beam forms

William Crooks developed the Crook’s Tube A tube with sealed gases and metal

plates at the end Run a current through the metal, and

a glowing beam forms

Schematic of a cathode ray tube.

Schematic of a cathode ray tube.

1897 - Sir J.J.Thompson1897 - Sir J.J.Thompson

Thompson proposed that the cathode ray formed in the tube is a stream of negatively charged particles

Key idea - ELECTRONS Showed that all cathode rays are electrons

regardless of the type of gas in the tube Atoms have parts that are negatively charged Since atoms are neutral, they must also have

positively charged areas Gave rise to the plum pudding model of the

atom

Thompson proposed that the cathode ray formed in the tube is a stream of negatively charged particles

Key idea - ELECTRONS Showed that all cathode rays are electrons

regardless of the type of gas in the tube Atoms have parts that are negatively charged Since atoms are neutral, they must also have

positively charged areas Gave rise to the plum pudding model of the

atom

Plum Pudding model of an atom.

Plum Pudding model of an atom.

1886 - Goldstein1886 - Goldstein

E. Goldstein discovered a positively charged particle.

Called them PROTONS Work was largely ignored

E. Goldstein discovered a positively charged particle.

Called them PROTONS Work was largely ignored

1909 - Ernst Rutherford1909 - Ernst Rutherford

Rutherford physicist who experimented with the positively charged particle

He figured Atoms have no charge Electrical charges are properties of matter Electrical charges exist in single whole

number units + or - (no fractions) Electrical Charges cancel each other,

therefore a + and a - together = neutral atom

Rutherford physicist who experimented with the positively charged particle

He figured Atoms have no charge Electrical charges are properties of matter Electrical charges exist in single whole

number units + or - (no fractions) Electrical Charges cancel each other,

therefore a + and a - together = neutral atom

Rutherford’s experiment. Rutherford’s experiment.

Results of foil experiment if Plum Pudding model had been correct.Results of foil experiment if Plum Pudding model had been correct.

Actual Results. Actual Results.

Rutherford’s modelRutherford’s model

Key Idea -NUCLEAR ATOM All of the mass of the positive

particles (protons) is at the center region of the atom

Center region called the NUCLEUS Electrons surround the nucleus in a

“cloud”

Key Idea -NUCLEAR ATOM All of the mass of the positive

particles (protons) is at the center region of the atom

Center region called the NUCLEUS Electrons surround the nucleus in a

“cloud”

1913 - Niels Bohr1913 - Niels Bohr

Danish Physicist Rutherford’s model did not work

because the electrons are so small compared to the positive mass in the center of the atom

Danish Physicist Rutherford’s model did not work

because the electrons are so small compared to the positive mass in the center of the atom

Bohr’s AtomBohr’s Atom

There are certain energy levels in the space of the electron cloud that mathematically allow the electron to stay in the cloud (not crash into the nucleus)

Key idea - There are certain ORBITS in which an electron can travel around the nucleus without losing energy

There are certain energy levels in the space of the electron cloud that mathematically allow the electron to stay in the cloud (not crash into the nucleus)

Key idea - There are certain ORBITS in which an electron can travel around the nucleus without losing energy

Bohr’s atom con’tBohr’s atom con’t

Suggested circular orbits The farther away from the nucleus,

the higher the energy level Under normal conditions, electrons

are arranged in the GROUND STATE. In the ground state, the electrons occupy the lowest energy level closest to the nucleus

Suggested circular orbits The farther away from the nucleus,

the higher the energy level Under normal conditions, electrons

are arranged in the GROUND STATE. In the ground state, the electrons occupy the lowest energy level closest to the nucleus

All models have problemsAll models have problems

All models are not exactly correct, but they lead to further science and discovery

All have important key ideas

All models are not exactly correct, but they lead to further science and discovery

All have important key ideas

We now know…We now know…

Atoms are made up of subparticles Atoms are divisible, but not by

ordinary chemical means Atoms of elements can vary

(isotopes) Electrons reside in ORBITALS, not

orbits

Atoms are made up of subparticles Atoms are divisible, but not by

ordinary chemical means Atoms of elements can vary

(isotopes) Electrons reside in ORBITALS, not

orbits