Imagine a particle of mass m, constrained to move along the x-axis, subject to some specified force F(x, t). The program of classical mechanics is to deter- mine the position of the particle at any given time: x(t). Once we know that, we can figure out the velocity (\( v=\frac{dx}{dt}\) ), the momentum (p = mv), the kinetic energy ( \( T=\frac{1}{2}mv^2 \) ), or any other dynamical variable of interest. And how do we go about determining x(t)? We apply Newton's second law: F = ma. (For conservative systems the only kind we shall consider, and, fortunately, the only kind that occur at the microscopic level---the force can be expressed as the derivative of a potential energy function, \( F=-\frac{\partial V}{\partial x} \) , and Newton's law reads \( m\frac{d^2x}{dt^2}=-\frac{\partial V}{\partial x} \) .) This, together with appropriate initial conditions (typically the position and velocity at t 0), determines x(t). Quantum mechanics approaches this same problem quite differentl
1. Atom Netral
Atom yang tidak bermuatan listrik.proton = elektron = nomor atom
neutron = massa atom - nomor atomContoh :
Tentukan jumlah proton, elektron, dan neutron unsur natrium dan magnesium!
Jawab :
natrium = \(^{23}_{11}Na \)
- proton = 11
- elektron = 11
- neutron = 23 - 11 = 12
magnesium = \(^{24}_{12}Mg \)
- proton = 12
- elektron = 12
- neutron = 24 - 12 = 12
2. Atom Bermuatan Positif (Kation)
Atom yang kelebihan proton karena berpindahnya elektron.proton = nomor atom
elektron = nomor atom - muatan
neutron = massa atom - nomor atomContoh :
Tentukan jumlah proton, elektron, dan neutron ion Ag+ dan ion Fe2+ !
Jawab :
argentum = perak = \(^{108}_{47}Ag\), maka untuk Ag+
- proton = 47
- elektron = 47 -1
- neutron = 108 - 47 = 61
ferrum = besi = \(^{56}_{26}Fe\), maka untuk Fe2+
- proton = 26
- elektron = 26 - 2 = 24
- neutron = 56 - 26 = 30
3. Atom Bermuatan Negatif ( Anion )
Atom yang kelebihan elektron karena berpindahnya elektron unsur lain ke dalam atom tersebut.proton = nomor atom
elektron = nomor atom + muatan
neutron = massa atom - nomor atomContoh :
Tentukan jumlah proton, elektron, dan neutron ion Br- dan ion S2- !
Jawab :
brom = \(^{80}_{35}Br\), maka untuk Br-
- proton = 35
- elektron = 35 + 1 = 36
- neutron = 80 - 35 = 45
sulfur = belerang = \(^{32}_{16}S\), maka untuk S2-
- proton = 16
- elektron = 16 + 2 = 18
- neutron = 32 - 16 = 16
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