1. Electical Charge And Atomic Structure Flashcards
Electric charge
- there exists a basic, smallest possible piece of charge
- 1.6x10^-19 Coulombs
Two types of charge quanta
That typified by e (negative charge)
That typified by protons (positive charge)
- both have same magnitude
- opposites attract, like charges repel
Coulomb’s law
- law obeyed by interaction force between two electric charges
- F=K Q1 Q2/ r^2
- constant is 9x10^9 Nm^2/C^2
The electric field
If at a certain point, a tiny, stationary positive charge experiences a force of electrical origin, we say that an electric field exists at that point
E=K Q/r^2
Electrical potential difference
Potential difference (PD) acquires by a united positive charge as it is moved from point A to point B is the work done against forces of electrical origin during the process
W=F ds
The atomic structure of matter
- all ordinary matter composed of individual entities called atoms
- all solids, liquids, and gasses are composed of atoms
- different types of atoms exist- each type called an element
- elements distinguished by physical/chemical properties of atoms
Each atoms consists of:
Central core- ‘nucleus’
- possesses most of atomic mass
- radius 10^-14 m
Surrounding cloud of electrons
- orbit nucleus
- Radii 10^-10 m
More facts about atoms
- most of an atom is empty space
- high energy photons can penetrate atoms without collisions
- atoms differ from one another ( number and arrangement of electrons)
- results in differences in physical/chemical properties
- chemical properties determined by electron structure
- for an atoms to be electrostatically neutral, number of electrons must equal number of protons
- atoms can easily lose or add electrons without altering nucleus-called ions
The nucleus
Composed of two functional particles:
- protons: positivity charged (same charge as electron 1.6x10^-19 C)
- neutrons: no charge
Atoms specified formulas:
Z^A X N
Z= atomic number (# of protons) A= mass number (# nucleons) X= chemical symbol for element N= neutron number
A= Z+N
Atoms classified into what categories?
- Isotopes
- Isotones
- Isobars
- Isomers
- Isotopes
- same number of protons, different number of neutrons
- May be stable or unstable
- stability depends on right mix of protons and neutrons
- same extranuclear structure but different nuclear masses
- if unbalanced, particle will be ejected
- ejection is called disintegration
- isotope is said to be radioactive
- can not be separated chemically
- as Z increases, number of isotopes and number of stable isotopes increases
- Isotones
Same number of neutrons (N) but different number of protons (Z)
- Isobars
Same number of neucleons(A) but different number of protons (Z)
- Isomers
Same number of protons (Z) as well as neutrons (N)
Identical atoms except differ in nuclear energy state
What are the 4 forces in nature?
- Electromagnetic
- Gravitational
- Strong nuclear
- Weak nuclear
Nuclear forces
- how are protons/neutrons held together in nucleus
- in nucleus magnetic/gravitational forces are weak
- electrostatic force strong but repulsive
- nuclear force responsible for binding
- nuclear force much stronger than electrostatic
- nuclear force is short range
- at large distance, force on positive charges particle by nucleus is repulsive
- as charged particle moves closer, nuclear forces dominate (attraction)
- Neutron is neutral spring electrostatic repulsion absent
- no region in which neutron is repelled by nucleus
- easier to move neutron into nucleus
Nuclear energy levels
Shell model of nucleus
- assumes nucleons arranges in shells
- shells represent discrete energy levels
- if energy imparted, raised to excited state
- upon returning to lower energy state, emits energy
- sometimes energy radiated in steps
Distribution of orbital electrons
Inner most orbital K shell then LMNO
Maximum number of electron in orbit is 2n^2 (n= orbit number)
K=2
L=8
M=18
N=32
Atomic energy levels
Quantum mechanics:
- e has finite probability of being anywhere in space
- most probable location: near orbital described above
- orbits have no real defined path-only probabilities
- energy of atoms is a real quantity
Electricity and magnetism
Electric fields:
Stationary charges particle yields a time invariant electric field
Moving charge(current) yields time varying electric field
Magnetic fields
Constant current yields a time invariant magnetic field
Counter part of the electric field
Alternating current yields a time varying magnetic field
X-rays and gamma rays- what are they?
- X-rays and gamma rays are identical in nature and properties
- electromagnetic radiation
- time varying fields of electrical and magnetic energy
- differ only in way in which produced
Examples of electromagnetic radiation
- radio waves
- radar
- visible light
- X-rays
- gamma rays
Same velocity but different wavelength
Radio waves: 3x10^4cm
Visible light: 5x10^-5
X-rays: 1x10^-8 cm
Ionizing radiation
- used in the treatment of cancer
- individual photon energy is large
- individual photon have enough energy to break molecular bonds and initiate biological change
- eg xrays, gamma rays
Non-ionizing radiation
- individual photon energy is small
- energy is transformed into heat or mechanical energy
- much greater quantities required to produce damage
- eg radio waves, radar, visible light
Difference between X-rays and gamma rays
Xrays
-produced extranuclearly
-Decelerating charged particle, chance of producing an X-ray
- electron passing close to nucleus
-bombard target with high energy electrons
X-ray tube (KeV) and linear accelerator(MeV energies)
Difference between X-rays and gamma rays
Gamma rays
- produced intranuclearly
- excess energy given off as unstable nucleus decays
- cobalt unit
