Elements Compounds and Mixtures- 1.What are the early ideas of atom?
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WHAT YOU ALREADY KNOW – Survey
Part (A) What you already know- Survey and Discussion.
Answer the questions below:
- Matter are made up of tiny particles called atoms. T/F
- All atoms in one matter have the same size and mass. For example, atoms of iron are all of same size and mass.
- All atoms of iron have the same chemical properties e.g. rusting T/F
- Atoms in different matter are different in size and shape. For example, atoms of iron are different from atoms of another metal such as magnesium. T/F
- Atoms are always in motion (either vibrating or moving around). T/F
- Rusting of iron is a chemical reaction. Y/N
- Water is a chemical. T/F
- Oxygen is a chemical T/.F
- Do you know what is an element? Y/N
- Do you know what is a compound? Y/N
- Oxygen is an element? T/F
- Do you know all chemicals listed on the periodic table are elements? Y/N
- Water is made up of two elements listed on the periodic table. Name these two elements. _________ and ________
- Do you know the formula for water? Y/N Write down the formula for water: _____
- Do you know water is not an element but a compound? Y/N Do you know why Y/N
- Have you heard about protons, neutrons, electrons? Y/N
- Rocks and minerals are chemicals? T/F
- Gold and copper are minerals and are elements and are listed in the periodic table. . T/F
- Do you know that pencil lead is made from the element, carbon? Y/N
- Carbon dioxide is made when two elements, carbon and oxygen combined in a chemical reaction. Y/N
PART (B) HISTORY of ATOMS – What were the early ideas? Who
HISTORY OF ATOMS – What were the early ideas of atoms?
Democritus (460-370 B.C.) Ancient Greece
His ideas of atoms:
- Matter was made up of tiny solid particles he called atomos.
- Different matter is made up of atomos that have different size and shape,
- Changes in matter are caused by a changing of the grouping of atomos, not in changing the atomos themselves.
Main idea: Democritus introduce the idea that matter is made up of atoms. All atoms of same matter are identical. Atoms of different matter are different.
Dalton, England: (1803) Ideas of atom:
- Atoms are solid spheres.
- Each atom has a mass.
- Atoms of same elements have the all same mass.
- Atoms are rearranged in a chemical reaction
- Compounds are formed when two or more different kinds of atoms join together.
Main idea:
Atoms of same elements have the all same mass, atoms can be rearrangeed in a chemical reaction to form compounds.
JJ Thomson: (1897)
- He discovered the electron in 1897.
- His idea showed that the atom contained smaller pieces, whereas Dalton had thought that atoms could not be broken down into anything simpler.
- His experiment using a cathode ray tube provides more thorough understanding of the properties of an electron (its mass compared with its electrical charge) and its properties.
Ernest Rutherford’s nuclear atom (1911)
- Ernest Rutherford used experimental evidence to show that an atom must contain a central nucleus.
- Rutherford assumes that electrons are located outside the nucleus.
- This was further evidence that an atom contained smaller particles called subatomic particles
- This experiment introduces the nucleus and its properties, and shed more light on the contents of the atom.
Bohr’s electron orbits (1922)
- Niels Bohr further developed Rutherford’s nuclear atom model. He used experimental evidence to support the idea that electrons occupy particular orbits or shells around the nucleus of an atom.
- The development of the theory of atomic structure is an example of:
- How a theory may change as new evidence is found
- How a scientific explanation is provisional but may become more convincing when predictions based on it are confirmed later on
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