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4-1: Introduction to Atoms

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1 4-1: Introduction to Atoms
How did the atomic theory develop and change into the modern model of the atom?

2 Anticipatory Set Here come the atoms!

3 California Standards Science Standard 8.3.a: Students know the structure of the atom and know it is composed of protons, neutrons, and electrons. Science Standard 8.7.b: Students know each element has a specific number of protons in the nucleus (the atomic number) and each isotope of the element has a different but specific number of neutrons in the nucleus.

4 Input atom: smallest particle of an element.
electron: negatively charged particles in an atom. nucleus: the central core of an atom proton: positively charged particles in an atom’s nucleus. energy level: the specific amount of energy an electron has.

5 Input neutron: small particle in the nucleus of an atom with no electrical charge atomic number: the number of protons in the nucleus of an atom. isotope: atoms of the same element that have different numbers of neutrons. mass number: the sum of the protons and neutrons in the nucleus of an atom.

6 Input Development of Atomic Theory
Atomic theory grew as a series of models that developed from experimental evidence. As more evidence was collected, the theory and models were revised. The atom is the smallest particle of an element. Around 430 B.C., a Greek philosopher, Democritus, proposed the idea that matter is formed of small pieces that could not be cut into smaller parts. He used the word atomos which means “uncuttable” for those smallest pieces.

7 Input & Modeling Dalton’s Atomic Theory
Dalton thought that atoms were like smooth, hard balls that could not be broken into smaller pieces.

8 Input & Modeling Dalton’s Atomic Theory
All elements are composed of atoms that cannot be divided. All atoms of the same element are exactly alike and have the same mass. Atoms of different elements are different and have different masses. An atom of one element cannot be changed into an atom of a different element. Atoms cannot be created or destroyed in any chemical change, only rearranged. Every compound is composed of atoms of different elements, combined in a specific ratio.

9 Input & Modeling Thomson’s Atomic Theory
Thomson suggested that atoms had negatively charged electrons embedded in a positive sphere. In 1897, English scientist J.J. Thompson found that atoms contain negatively charged particles. The negatively charged particles later became known as electrons.

10 Input & Modeling Rutherford’s Atomic Theory
According to Rutherford’s model, an atom was mostly empty space. In 1911, Ernest Rutherford found evidence that countered Thompson’s model. His team discovered the positive charge (proton) in an atom is clustered in the center (nucleus).

11 Input & Modeling Bohr’s Atomic Theory
In 1913, Niels Bohr, a Danish scientist, suggested that electrons move in specific orbits around the nucleus of an atom.

12 Input & Modeling Cloud Model
In the 1920’s, scientists determined that electrons do not orbit the nucleus like planets, but rather could be anywhere in a cloudlike region. An electron’s movement is related to its energy level, or the specific amount of energy it has. Electrons of different energy levels are likely to be found in different places.

13 Input & Modeling The Modern Atomic Model
In 1932, English scientist James Chadwick discovered another particle, the neutron, in the nucleus of atoms.

14 Input & Modeling The Modern Atomic Model
At the center of the atom is a tiny, massive nucleus containing protons and neutrons. Surrounding the nucleus is a cloudlike region of moving electrons. The particle was difficult to detect because it has no charge.

15 Input Particles in an Atom
An atom is composed of positively charged protons, neutral neutrons, and negatively charged electrons. Protons and neutrons are about equal in mass. An electron has about 1/2,000 the mass of a proton or neutron.

16 Input Isotopes Atoms of all isotopes of carbon contain six protons and six electrons, but they differ in their number of neutrons. Carbon-12 is the most common isotope.

17 Check for Understanding
What is located in a cloudlike region surrounding the nucleus in the modern atomic model? electrons According to Dalton, all elements are composed of atoms that cannot be ___. divided

18 Guided Practice Independent Practice Answer #1-4 Finish the worksheet.
Complete the extension. Rutherford Dalton Bohr Thomson

19 EXTENSION Write a detailed SUMMARY of the section and complete the UNANSWERED QUESTIONS section of your notes. Choose two of the remaining Depth & Complexity ICONS in your notes and explain how they relate to this section. Finish the Development of Atomic Theory Timeline Booklet.

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