1. What Are Elements? Crash Course Kurzgesagt
Topic 3

2. I Can… statements
I can distinguish between observation and theory, and provide examples of how models and theoretical ideas are used in explaining observations
Example: Describe how observations of electrical properties of materials led to ideas about electrons and protons; describe how observed differences in the densities of materials are explained, in part, using ideas about the mass of individual atoms)

3. History of 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 any further

4. History of 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.

5. History of Elements
Aristotle then stated that everything was made of earth, fire, air and water. Since he was well respected, his description of matter was preferred for 2000 years.

6. From Alchemy…
For the next 2000 years, alchemists, people who were part magician, part scientist, carried out experiments.
The study of alchemy is known as a pseudo-science. It is a not a real science because it contains magic.
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.

7. … to Chemistry
From the 1500s onwards, scientific experiments were carried out and Sir Francis Bacon proposed that science should be based on experimental evidence instead of thoughts and ideas.
Robert Boyle researched and realized that elements formed compounds. He was convinced that matter was made of smaller particles (just like Democritus had proposed) and that that the purpose of chemistry was to determine the types of particles making up each substance.
The work of these two men led to continued research on the topic.

8. In the 17th and 18th centuries, scientists continued to search for elements.
Antoine Lavoisier is known as the “father of modern chemistry.”
He heated, burned, mixed and cooled matter and found 23 pure elements.
Unfortunately, he was then beheaded.

9. Antoine Lavoisier
He was very careful with his experiments and kept very organized observations and data.
Since he measured the masses of the matter he worked with, he developed the… law of conservation of mass.
Law of Conservation of Mass
In a chemical change, the total mass of the new substances is always the same as the total mass of the original substances.

10. Antoine Lavoisier
His accurate measuring also led others to determine the Law of Definite Composition
Law of Definite Proportions
Compounds are pure substances that contain two or more elements combined together in fixed (or definite) proportions
Examples
Water (H2O) always contains 89% Hydrogen and 11% Oxygen.
Hydrogen Peroxide (H2O2) always contains 6% Hydrogen and 94% Oxygen.

11. Dalton’s Atomic Theory
Earlier, we mentioned the Particle Model of Matter – but that was revised because it didn’t explain everything.
John Dalton created a new way to think about substances.
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 than another element.

12. An element is a pure substance made up of one type of particle, or atom. Each element has its own distinct properties and cannot be broken down into simpler substances by means of chemical change.
A compound is a pure substance that is made up of two or more elements chemically combined together. Compounds can be broken down into elements again by chemical means.

13. Laws, Theories, Models and Observations
Law – an action or condition that has been observed so consistently that scientists are convinced it will always happen
Theory – an explanation of an event that has been supported by consistent, repeated experimental results and has therefore been accepted by a majority of scientists
Model – a mental image, used as a building block that helps to explain an event.
Observation – the use of the senses to gather information.

14. Laws, Theories, Models and Observations
Time and more experiments Observations Hypothesis Experiments Theory Revised Theory Repeated as many Revised times as necessary Hypothesis

15. History of Atomic Models
Crash Course
Scientist(s)
Model
J.J. Thomson
Plum Pudding Model
Hantaro Nagaota and Ernest Rutherford
Planetary Model
Niels Bohr
Revised Planetary Model
Various
Current Model

16. Bohr Diagram We continue to look at Niels Bohr’s diagram of the atom
Electrons in the outer shell are called valence electrons
An atom is the most stable when the outer shell is full
Atoms will give or take electrons to make their outer shell full.
Electron shells
1st shell: 2 e-
2nd shell: 8 e-
3rd shell: 8 e-
4th shell: 18 e-
Electrons (-1)
Inside nucleus:
Protons (+1)
Neutrons (N)
Nucleus

17. Example Once an atom gives or takes electrons, it becomes an ion.
The charge on the ion depends on how many electrons are transferred.
This nitrogen atom has 5 electrons in its outer shell – it can give 5 or take 3 to make its outer shell full.
What is easier? Take 3 electrons.
If it takes 3 negative electrons, the charge becomes We write this as N-3.

20. Practice Element: Oxygen
Components: 8 protons, 7 neutrons, 8 electrons
Element symbol: O
Bohr Diagram:
Electron transfer: Take 2 e-
Ion symbol: O-2

21. Practice Element: Components: Element symbol: Bohr Diagram:
Electron transfer:
Ion symbol: