1. Topic 3
What are Elements?

2. What are Elements? Meet the elements:
Greek philosophers observed that rock could be broken down into smaller and smaller pieces until it became powder.
They then wondered how many times you could continue to break the particles of powder down until they couldn’t be broken down any further.

3. What are Elements?
Democritus described the smallest particle as atomos, meaning “indivisible.”
He believed that each type of material was made up of a different atomos.
These different particles gave materials their own unique set of properties. These could then be added to make new materials with their own properties.

4. Some history….
The original ‘elements’ were earth, air, fire and water.
Ancient Greek philosophers thought matter was made out of these four ‘elements’.
They thought all things were made from these four elements with varying degrees of hotness, coldness, dryness and wetness.

5. From Alchemy
For the next 2000 years, alchemists, people who were part magician, part scientist, carried out experiments.
They believed that they should be able to turn any metal into gold and they were not interested in understanding the nature of matter.
They did, however, perform some of the first chemistry experiments.
The study of alchemy is known as a pseudo-science. It is a not a real science because it contains magic.

6. What are Elements?
Chemistry was formed by trying to find elements and many scientists had lots of crazy ideas on trying to make gold.
Many thought they could turn lead or copper into gold and one guy even thought he could turn his urine into gold.

7. What are elements?
Well, we all know that didn’t happen….. So how did scientists search for elements???
I guess they first had to know what elements were…..

8. Elements vs. Compounds
An element is a pure substance made up of only one type of particle, or atom.
Each element has its own unique set of distinguishing properties and cannot be broken down into simpler substances by means of a chemical change.

9. Elements vs. Compounds
A compound is a pure substance made up of 2 or more elements chemically combined together.
Compounds can be broken down into the elements that they are composed of.

10. The Law of Definite Composition
I guess they first had to know what elements were….. I guess they first had to know what elements were…..
The Law of Definite Composition
Compounds are pure substances that contain two or more elements combined together in fixed (or definite) proportions
What does this mean???
Water is made of hydrogen and oxygen
11% hydrogen, 89% oxygen
Hydrogen Peroxide is made of hydrogen and water
6% hydrogen and 94% oxygen
Hydrogens have a mass of 1.007g each and Oxygen has a mass of 15.99g so percentage wise 88%

11. Electrolysis
Using a “voltaic pile” scientists could separate compounds.
Voltaic piles are still used today – we call them batteries.
The voltaic pile, invented by Alessandro Volta in 1800, was the first electric battery. Its invention can be traced back to an argument between Volta and Luigi Galvani, Volta’s fellow Italian scientist who had gained notoriety for his experiments on frog legs.
Galvani found that the legs of a frog would contract when forming a circuit with two different kinds of metal. Galvani contended that this phenomenon resulted from an inherent “animal electricity,” an electrical fluid present in the animal itself. Volta disagreed. His own experiments proved that this electric stimulation was ultimately the result of the different metals in the circuit and the electrolyte – that is, the frog legs – between them.

12. Electrolysis
Early scientists used voltaic piles to pass electricity through water.
Breaking down compounds into their separate elements by shooting electric current through the compound is called electrolysis.
Electrolysis was used to isolate potassium, sodium, magnesium, calcium, strontium and barium.
Early scientists used voltaic poles to pass electricity through water. They discovered that hydrogen and oxygen gasses were produced and that the water level fell slightly.
Scientists inferred that the water had been decomposed into hydrogen and oxygen.
The process of decomposing a chemical compound by passing an electric current through it is called Electrolysis.

13. CHEMISTRY’S MOST WANTED…
#1 - DALTON
Dalton thought of atoms as billiard balls.
He drew pictures of water with equal numbers of smaller hydrogen and larger oxygen atoms.
The particle model of matter worked for early scientists but it cannot explain what happens in the electrolysis of water. The properties of the compound (water) are different than the properties of the elements that make it up (H and O).
Therefore the particles of water must be different from the particles of hydrogen and the particles of oxygen.
In the early 1800s John Dalton introduced a new way of explaining chemical facts and laws in his atomic theory.

14. Dalton’s Atomic Theory
All matter is made up of small particles called atoms.
Atoms cannot be created, destroyed, or divided into smaller particles.
All atoms of the same element are identical in mass and size. Atoms of one element are different in mass and size form the atoms of other elements.
Compounds are created when atoms of different elements link together in a definite proportion.
Dalton’s model uses the idea that elements are different because their particles (or atoms) are different. This model led to more accurate definitions of element and compound.

15. Dalton’s Definitions
Element – pure substance made up of one type of particle or atom. Each element has its own distinct properties and cannot be broken down by means of chemical change.
Compound – pure substances that are made up of two or more different elements chemically combined together. Compounds can be broken down into elements by chemical means.

16. CHEMISTRY’S MOST WANTED…
#2 - THOMSON
Thought of atoms as negatively charged electrons stuck to a positively charged mass
“Raisin Buns”
“Plum Pudding”
British physicist JJ Thomson studied rays in gas discharge tubes. He inferred the rays were streams of negatively charged particles. Since atoms do not normally have a charge Thomson reasoned there must also be positively charged particles in the atom.

17. CHEMISTRY’S MOST WANTED…
#3 - RUTHERFORD
Thought the entire mass of an atom was in the center of the atom (called the atomic nucleus)
He thought the rest of the atom was just empty space
Rutherford was from New Zealand (though he worked at MCGill in Montreal).

18. Rutherford’s Model
He called the positively charged particles in the center of the atom protons.
He called the negatively charged particles floating around the atomic nucleus, electrons.

19. CHEMISTRY’S MOST WANTED…
#4 - BOHR
Pictured the atom like a mini solar system.
Electrons rotated around the nucleus like the planets around the sun in things called electron shells.
Neils Bohr studied with Rutherford.

20. Chemistry as Science
Bohr (1922) presents the electron shell model (Nobel Prize)
Electron shells are specific circular orbits that electrons follow around atomic nuclei
TED: The uncertainty of electrons

21. Chadwick Later on, Chadwick discovered Neutrons.
He said these particles didn’t have a charge but helped make up the mass of the atom.
Neutrons are in the atomic nucleus with the protons.

22. The story so far: Matter has mass and takes up space
Matter can be pure or a mixture
Matter is made up of tiny particles called atoms
Atoms cannot be broken down, created nor destroyed
Elements are made up of unique atoms.
Carbon atoms are different than Oxygen atoms

23. The Modern Atom
Chadwick discovers that the nucleus of an atom contains protons and neutrons (after 1922)
Nucleus is the positively charge center of an atom, containing protons and neutrons
Protons are the positively charged particles in the atomic nucleus
Neutrons are the neutrally charged particles in the atomic nucleus
James Chadwick was an English Physicist who studied with Rutherford.