The Structure of the Atom

1. The Structure of the Atom Chapter 3 Section 2

2. Introduction Terms • _________: the smallest particle of an element that retains the chemical properties of that element • _______: very small region located at the center; composed of proton(s) and usually one or more neutrons • _________: a positively charged particle in the nucleus

3. Introduction Terms • __________: a neutral particle found in the nucleus • _________: a negatively charged particle found in a region surrounding the nucleus • Subatomic particles: _______________ _________________

4. Subatomic Particles Detected • In 1897, J.J. Thomson used the ______ __________to deduce the presence of a _____________ charged particle: the ________________.

5. Thomson’s Model of the Atom • J.J. Thomson proposed a subatomic model of the atom in 1903. • Thomson proposed that the _________________were distributed evenly throughout a homogeneous sphere of positive charge. • This was called the “_____________” model of the atom. Think of a chocolate chip cookie.

6. Rutherford’s Gold Foil Experiment • Rutherford’s student fired alpha particles (helium nuclei; positive charge) at thin gold foils. If the “plum pudding” model of the atom was correct, α-particles should pass through ______________ • However, some of the alpha particles were _____________________

7. Rutherford’s Findings • __________ of the particles passed right through. • A few particles were ______________. • Some of those were _________ deflected. “Like howitzer shells bouncing off of tissue paper

8. Explanation of Scattering • Most of the alpha particles passed through the foil because _________________________ • At the center of an atom is the _______________, which contains the atom’s ______________. • The α-particles that bounced backwards did so after striking the ______________.

9. Rutherford's Model of the Atom • Rutherford proposed a new model of the atom: • _________________________________________ _________________________________________ • An atom has a diameter of about 1 × 10-8 cm and the nucleus has a diameter of about 1 × 10-13 cm. • If an atom were the size of the Superdome, the nucleus would be the size of a marble.

10. Subatomic Particles Revisited • Based on the heaviness of the nucleus, Rutherford predicted that it must contain ________ particles in addition to protons. • Neutrons, n0, were discovered officially in the 1930s by James Chadwick. A neutron is about the size of a _________without any ____________.

11. Conclusions of the Experiment • The nucleus is __________ • The nucleus is ___________ • The nucleus is __________________ • The atom is mostly _______________

12. Rutherford’s Model • All the __________charge, and almost all the __________is concentrated in a small area in the center. He called this a _____________. • The nucleus is composed of __________ and _____________. • The ____________ are distributed around the nucleus, and occupy most of the atom’s _____________. • His model was called a “_______________”.

13. Summary of Models • Greeks- Philosophical (thought) idea of the atom. The word “atom” originated in Greek. • Dalton- Experiments and postulates about the existence of atoms- Picture as a marble or solid sphere that makes up matter (a brick in a wall). • Thomson- Idea of electron- Small with negative charge- Cathode ray tube experiment- “Plum Pudding Model” • Rutherford- Nucleus with positive charge (Protons/ Neutron comes later)- Gold foil experiment- Nucleus very dense with much of atom as “empty space.”- “Nuclear” Model

14. Other Interesting Stuff • Atoms are electrically __________if they contain an equal number of _______ and ____________. • The number of ________ determines the atom’s ____________. This is its ______ ____________. • There are other subatomic particles, but they have little effect on the chemical properties of matter.

15. Forces in the Nucleus • Protons, with their positive charge, would be expected to ___________each other in the nucleus. • When they are extremely close to each other, there is a strong attraction. It is given the name the “_______________ _________.” • A similar attraction exists when neutrons are present.

16. Sizes of Atoms • Electrons occupy the outer region known as the _______________. • Radius of an atom is the distance from ___________________to the outer portion of the ________________. • Atomic radii are _____________so they are usually measured in picometers. Remember, 1 x 1012 pm = 1 m