Tuesday, March 16, 2010
Behaviour of Protons, Neutrons and Electrons in Electric and Magnetic fields
The law of electrostatics states that consistently demonstrate that opposite charges attract.
There fore, we deduce with the law of electrostatics:
Electrons are negatively charged and are therefore attracted to the positive plate in an electric field.
Neutrons are unaffected in an electric field.
Protons and Electrons will follow circular paths in magnetic fields. The force due to the magnetic field is a centripetal force. Neutrons will be unaffected because it has no charge.
Electronic Configuration
The relative energies of various orbitals of single electrons depend on the value of the principal quantum number 'n' and is independent of the value of 'l'. This can be shown by an arrangement known as energy level diagram. The diagram given below illustrates the relative energy of various energy levels for hydrogen and hydrogen like atoms.
For a particular main energy level, the orbital having higher value of the azimuthal quantum number 'l' has higher energy. In general, energies of orbitals belonging to the same main energy level follow the order, 's' < 'p'< 'd'< 'f' .
Shape of s and p orbitals
The energies of atomic orbitals also describe their shapes. The shapes are uncertain, but predictions have been made by experimentation. Another difficult task is describing where an electron is. We can think of it as a wave, and describing its exact location is impossible for us to comprehend. Instead, we can think of it as the statistical probability of the electron being found at a particular place. An electron cloud is used for showing the probability of where an electron is using a dot-density diagram. The denser the dots are in the diagram, the more probability that an electron could be found there.
For example, these are dot-density diagrams for the s and p orbitals (cross sections):
Electron density relates to how much of an electron's charge is packed into a given volume. In dense places on the dot-diagram, there is a high concentration of electrical charge.
An s orbital's shape is spherical, but the p orbital's shape is quite different. They have two lobes extending out into three dimensional space. Since there are 3 p orbitals per energy level, the lobes extend out along the x-axis (px orbital), the y-axis (py orbital), and the z-axis (pz orbital).
Writing Electronic Configuration
For writing electron configurations, the key is to use the periodic table. To write the configuration of S2-, look at what element as has 2 more electrons than S and write the electronic configuration of that element (in this case [Ar]). For Ca2+ look at the element that has 2 fewer electrons than Ca (since Ca would have to lose 2 electrons to become a +2 ion).
The electronic configurations for the first 20 elements are:
For a particular main energy level, the orbital having higher value of the azimuthal quantum number 'l' has higher energy. In general, energies of orbitals belonging to the same main energy level follow the order, 's' < 'p'< 'd'< 'f' .
Shape of s and p orbitals
The energies of atomic orbitals also describe their shapes. The shapes are uncertain, but predictions have been made by experimentation. Another difficult task is describing where an electron is. We can think of it as a wave, and describing its exact location is impossible for us to comprehend. Instead, we can think of it as the statistical probability of the electron being found at a particular place. An electron cloud is used for showing the probability of where an electron is using a dot-density diagram. The denser the dots are in the diagram, the more probability that an electron could be found there.
For example, these are dot-density diagrams for the s and p orbitals (cross sections):
Electron density relates to how much of an electron's charge is packed into a given volume. In dense places on the dot-diagram, there is a high concentration of electrical charge.
An s orbital's shape is spherical, but the p orbital's shape is quite different. They have two lobes extending out into three dimensional space. Since there are 3 p orbitals per energy level, the lobes extend out along the x-axis (px orbital), the y-axis (py orbital), and the z-axis (pz orbital).
Writing Electronic Configuration
For writing electron configurations, the key is to use the periodic table. To write the configuration of S2-, look at what element as has 2 more electrons than S and write the electronic configuration of that element (in this case [Ar]). For Ca2+ look at the element that has 2 fewer electrons than Ca (since Ca would have to lose 2 electrons to become a +2 ion).
The electronic configurations for the first 20 elements are:
He 1s2
Li 1s22s1
Be 1s22s2
B 1s22s22p1
C 1s22s22p2
N 1s22s22p3
O 1s22s22p4
F 1s22s22p5
Ne 1s22s22p6
Na 1s22s22p63s1
Mg 1s22s22p63s2
Al 1s22s22p63s23p1
Si 1s22s22p63s23p2
P 1s22s22p63s23p3
S 1s22s22p63s23p4
Cl 1s22s22p63s23p5
Ar 1s22s22p63s23p6
K 1s22s22p63s23p64s1
Ca 1s22s22p63s23p64s2
Protons, Neutrons and Electrons
This table easily identifies protons, neutrons and electrons in terms of their relative charges and relative masses.
Different atoms are distinguished by their numbers of protons and neutrons. We write the symbols using the following notation:
A is called the nucleon number, or the mass number. It is the total number of nucleons.
Z is the proton number or the atomic number, which is the number of protons. The number of protons determines the element.
We can determine the number of neutrons simply by subtracting the proton number from the nucleon number. ( No of neutrons = A – Z) Atomic particles are always in whole numbers.
When you add the number of Protons and Neutrons together, we get the nucleon number
Isotopes
Isotopes are different types of atoms of the same chemical element, each having a different number of neutrons. In a corresponding manner, isotopes differ in mass number (or number of nucleons) but not in atomic number.
Deducing the number of protons, neutrons and electrons from proton number and nucleon number
To find the number of protons in an atom or ion, we look at the proton number.
To find the number of neutrons in an atom or ion, we subtract the proton number from the nucleon number.
To find the number of electrons in an atom or ion, we look at the proton number, then add to the subtract the charge. (E.G. Ca2+ - 20-2=18 )
Distribution of mass and charges within an atom
The mass of an atom at rest is often expressed using the unified atomic mass unit (u), which is also called a Dalton (Da). This unit is defined as a twelfth of the mass of a free neutral atom of carbon-12, which is approximately 1.66 × 10−27 kg.
Electrons have an electric charge of −1.602×10−19 coulomb, which is used as a standard unit of charge for subatomic particles. Within the limits of experimental accuracy, the electron charge is identical to the charge of a proton, but with the opposite sign. As the symbol e is used for the elementary charge, the electron is commonly symbolized by e−, where the minus sign indicates the negative charge. The positron is symbolized by e+ because it has the same properties as the electron but with a positive rather than negative charge.
| | Location | Relative mass | Relative charge |
| Proton | Inside the nucleus | 1 | 1 |
| Neutron | Inside the nucleus | 1 | 0 |
| Electron | Outside the nucleus | 1/1836 | -1 |
Different atoms are distinguished by their numbers of protons and neutrons. We write the symbols using the following notation:
A is called the nucleon number, or the mass number. It is the total number of nucleons.
Z is the proton number or the atomic number, which is the number of protons. The number of protons determines the element.
We can determine the number of neutrons simply by subtracting the proton number from the nucleon number. ( No of neutrons = A – Z) Atomic particles are always in whole numbers.
When you add the number of Protons and Neutrons together, we get the nucleon number
Isotopes
Isotopes are different types of atoms of the same chemical element, each having a different number of neutrons. In a corresponding manner, isotopes differ in mass number (or number of nucleons) but not in atomic number.
Deducing the number of protons, neutrons and electrons from proton number and nucleon number
To find the number of protons in an atom or ion, we look at the proton number.
To find the number of neutrons in an atom or ion, we subtract the proton number from the nucleon number.
To find the number of electrons in an atom or ion, we look at the proton number, then add to the subtract the charge. (E.G. Ca2+ - 20-2=18 )
Distribution of mass and charges within an atom
The mass of an atom at rest is often expressed using the unified atomic mass unit (u), which is also called a Dalton (Da). This unit is defined as a twelfth of the mass of a free neutral atom of carbon-12, which is approximately 1.66 × 10−27 kg.
Electrons have an electric charge of −1.602×10−19 coulomb, which is used as a standard unit of charge for subatomic particles. Within the limits of experimental accuracy, the electron charge is identical to the charge of a proton, but with the opposite sign. As the symbol e is used for the elementary charge, the electron is commonly symbolized by e−, where the minus sign indicates the negative charge. The positron is symbolized by e+ because it has the same properties as the electron but with a positive rather than negative charge.
Learning Objectives
(a) identify and describe protons, neutrons and electrons in terms of their relative charges and
relative masses
(b) deduce the behaviour of beams of protons, neutrons and electrons in both electric and
magnetic fields
(c) describe the distribution of mass and charges within an atom
(d) define proton (atomic) number and nucleon (mass) number
(e) interpret and use such symbols as
(f) deduce the numbers of protons, neutrons and electrons present in both atoms and ions given
proton and nucleon numbers (and charge)
(g) (i) describe the contribution of protons and neutrons to atomic nuclei in terms of proton
number and nucleon number
(ii) distinguish between isotopes on the basis of different numbers of neutrons present
(h) describe the number and relative energies of the s, p and d orbitals for the principal quantum
numbers 1, 2 and 3 and also the 4s and 4p orbitals
(i) describe the shapes of s and p orbitals
(j) state the electronic configuration of atoms and ions given the proton number (and charge)
relative masses
(b) deduce the behaviour of beams of protons, neutrons and electrons in both electric and
magnetic fields
(c) describe the distribution of mass and charges within an atom
(d) define proton (atomic) number and nucleon (mass) number
(e) interpret and use such symbols as
12
C
(f) deduce the numbers of protons, neutrons and electrons present in both atoms and ions given
proton and nucleon numbers (and charge)
(g) (i) describe the contribution of protons and neutrons to atomic nuclei in terms of proton
number and nucleon number
(ii) distinguish between isotopes on the basis of different numbers of neutrons present
(h) describe the number and relative energies of the s, p and d orbitals for the principal quantum
numbers 1, 2 and 3 and also the 4s and 4p orbitals
(i) describe the shapes of s and p orbitals
(j) state the electronic configuration of atoms and ions given the proton number (and charge)
Introduction
Welcome to our website on Atomic structure. This will provide information to allow for further learning .
Done by 3P1 Isaac Lim 06 and 3P1 Kee Zheng Hao 08
Done by 3P1 Isaac Lim 06 and 3P1 Kee Zheng Hao 08
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