Constituents of the atom

Size: px

Start display at page:

Download "Constituents of the atom"

Gilbert Dalton
6 years ago
Views:

1 Constituents of the atom From Plum Pudding to modern Physics

2 Review E=nhf E upper E lower =hf= hc/λ E n = 13.6/ n 2 ev Balmer series for Hydrogen: λ=b( n 2 / n ) Rydberg series: 1/λ =R( 1/ m 2 1/ n 2 ) What is missing?

3 Isotopes Recall the mass spectrometer, in which an atom is stripped of its electrons and accelerated through a voltage into a magnetic field. Scientists discovered that hydrogen nuclei had three different masses: Since the charge of the hydrogen nucleus is e, scientists postulated the cgrahamphysics.com existence 2015 of a neutral particle called the neutron, which added mass without charge.

Beryllium was bombarded with α parjcles, which produced a very penetrajng radiajon Chadwick showed that this radiajon consisted of neutrons Chadwick s discovery

4 Beryllium was bombarded with α parjcles, which produced a very penetrajng radiajon Chadwick showed that this radiajon consisted of neutrons Chadwick s discovery of the neutron James Chadwick Experimental demonstrajon of the Neutron, 1932 Nobel Prize, 1935 Chadwick isolated an uncharged parjcle with the same mass as a proton

5 Model of the atom Protons and neutrons are called nucleons

6 Isotopes The proton and neutron are called nucleons. Nucleons Proton [ Charge = 1e or just +1 ] Neutron [ Charge = 0e or just 0 ] For the element hydrogen, it was found that its nucleus existed in three forms: Isotopes Hydrogen Deuterium Tritium A set of nuclei for a single element having different numbers of neutrons are called isotopes. A particular isotope of an element is called a species or a nuclide.

Isotopes Isotopes have the same number of

is the same, isotopes have similar chemical

7 Isotopes Isotopes have the same number of protons, but different number of neutron The discovery of the neutron explained the existence of isotopes Because the proton number is the same, isotopes have similar chemical properjes The more neutrons are added, the heavier the element becomes

8 Isotopes A species or nuclide of an element is described by three integers: The nucleon number A is the total number of protons and neutrons in the nucleus. The proton number Z is the number of protons in the nucleus. It is also known as the atomic number. The neutron number N is the number of neutrons in the nucleus. It follows that the relationship between all three numbers is just A = Z + N nucleon relationship

9 Nuclides N = A - Z

10 Isotopes In nuclear physics you need to be able to distinguish the different isotopes. CHEMISTRY H NUCLEAR PHYSICS Mass Number = A H Protons = Z 1 H H FYI Since A = Z + N, we need not show N. And Z can be found on any periodic table. 2 N = Neutrons H hydrogen deuterium tritium hydrogen-1 hydrogen-2 hydrogen-3 3

SOLUTION: A = 65, Z = 29, so N = A Z = 65 29 = 36.

11 Isotopes PRACTICE: Which of the following gives the correct number of electrons, protons and neutrons in the neutral atom Cu? SOLUTION: A = 65, Z = 29, so N = A Z = = 36. Since it is neutral, the number of electrons equals the number of protons = Z = 29.

12 Isotopes PRACTICE: Ag-102, Ag-103 and Ag-104 are all isotopes of the element silver. Which one of the following is a true statement about the nuclei of these isotopes? A. All have the same mass. B. All have the same number of nucleons. C. All have the same number of neutrons. D. All have the same number of protons. SOLUTION: Isotopes of an element have different masses and nucleon totals. Isotopes of an element have the same number of protons, and by extension, electrons. This is why their chemical properties are identical.

Assume both ions travel at the same speed.

13 Isotopes PRACTICE: Track X shows the deflection of a singly-charged carbon-12 ion in the deflection chamber of a mass spectrometer. Which path best shows the deflection of a singlycharged carbon-14 ion? Assume both ions travel at the same speed. SOLUTION: Since carbon-14 is heavier, it will have a bigger radius than carbon-12. Since its mass is NOT twice the mass of carbon-12, it will NOT have twice the radius.

14 Fundamental Forces

Extremely Short Force Carrier: Gluon light, heat and charge

15 Fundamental forces and their properties STRONG ELECTRO-WEAK ELECTROMAGNETIC WEAK GRAVITY + + nuclear force STRONGEST Range: Extremely Short Force Carrier: Gluon light, heat and charge radioactivity freefall Range: Force Carrier: Photon Range: Short WEAKEST Range: Force Carrier: Graviton

16 Fundamental forces and their properties PRACTICE: The nucleus of an atom contains protons. The protons are prevented from flying apart by A. The presence of orbiting electrons. B. The presence of gravitational forces. C. The presence of strong attractive nuclear forces. D. The absence of Coulomb repulsive forces at nuclear distances. SOLUTION: It is the presence of the strong force within the nucleus.

There are 82 protons in a lead nucleus. Why doesn t the lead nucleus burst apart?

Question 32.1 The Nucleus There are 82 protons in a lead nucleus. Why doesn t the lead nucleus burst apart? a) Coulomb repulsive force doesn t act inside the nucleus b) gravity overpowers the Coulomb repulsive