1. Developing atomic theory

2. Learning goals
We are learning how the atomic theory developed over time.
We are learning of the contributions of various scientists to the atomic theory.

3. atoms
the smallest part of an element that has all of the element’s properties
modern term “atom” from Greek atomos
meaning indivisible

4. Atomic theory
the study of the nature of atoms and how they combine to form all types of matter.
helps to understand why there are different kinds of atoms
explains how atoms combine to form over 100 known elements and all other forms of matter, including compounds and mixtures.

5. Your task
Become an expert of a scientist who contributed to the discovery of the atom and their contribution to the atomic theory.
Share your acquired knowledge with your peers.

6. Early views Democritus (440 BCE) Aristotle
All matter can be broken down into smaller and smaller pieces until single indivisible particle
Atom – cannot be cut
Different sizes, constant motion, separated by empty space
Aristotle
Earth made of 4 basic substances: earth, water, air, fire
4 qualities: dry, wet, cold, hot

7. dalton All matter is made of small, indivisible particles called atoms
All the atoms of an element are identical in properties such as size and mass
Atoms of different elements have different properties
Atoms of different elements can combine in specific ways to form new substances

8. thompson
researched idea that atoms might be made from a combination of particles
discovered negative particles
reasoned there must be positive particles too
depicts the atom as a positive sphere with negative electrons scattered throughout it

9. rutherford discovered the nucleus, the centre of the atom
tiny positively charged part of the atom also contains most of the atom’s mass
determined nucleus to be very tiny compared to rest of atom
electrons surrounded the nucleus and occupied most of the atom’s volume, but they contained only a small fraction of the atom’s total mass

10. chadwick refined concept of nucleus
discovered nucleus contains neutral particles as well as positively charged particles
called neutrons
positively charged particles in the atom are called protons
each neutron in an atom has about the same mass as each proton

11. bohr
suggested electrons surround the nucleus in specific energy levels, called shells
discovered electrons jump between shells by gaining or losing energy
each shell can contain only a specific number of electrons
max number of electrons that can exist in each of the first three shells is two, eight, and eight

12. Quantum mechanical model
electrons do not exist as tiny points inside an atom
electrons exist in specific energy levels, but they surround the positively charged nucleus in a form resembling a cloud

13. Atom summary
all elements are composed of atoms, and one atom is the smallest unit of any element.
atoms themselves are made of different kinds of smaller particles, called subatomic particles
three subatomic particles are protons, neutrons, and electrons, and they have different properties

14. Properties of subatomic particles
Name
Symbol
Relative Mass
Electric Charge
Location
Proton p
1836 1+
nucleus
Electron e 1 1-
in energy levels surrounding nucleus
Neutron n
1837

15. Watch!
History of Atomic Theory

16. Learning goals
We are learning how the atomic theory developed over time.
We are learning of the contributions of various scientists to the atomic theory.