Tham khảo tài liệu 'sat ii physics (gary graff) episode 2 part 2', ngoại ngữ, ngữ pháp tiếng anh phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | CHAPTER 7 Note the negative sign. The electron must absorb to rise from the n 2 potential to the n 4 potential. Example The next problem is one where the electron emits energy and falls from a higher potential to a lower potential toward the ground state . An electron at n 3 emits energy as it falls from n 3 to n 1. How much energy did the electron lose n 5 n 4 n 3 n 2 n 1 Solution The energy emitted by the electron as it changes from n 3 to n 1 is AE E3 - E1 AE - AE AE Note the positive sign. When the electron falls to its ground state it emits all the energy it had absorbed to reach the excited state. The Nucleus All matter is made of atoms. Except for hydrogen atoms consist of protons and neutrons in the nucleus and the electrons that are always found outside the nucleus. Hydrogen is made of electrons and protons only. Atoms are electrically neutral when an atom has gained or lost electrons the result is an ion. The number of protons in the nucleus of an atom is the atomic number called the Z number. Because all atoms are electrically neutral this is the number of electrons too. All atoms of a particular element contain the same number of protons however they may have different numbers of neutrons. 220 Peterson s SATIISuccess Physics THE ATOM Hydrogen Proton Notice that the hydrogen deuterium and tritium above each have one proton and one electron. The difference between them is the number of neutrons in the nucleus. The sum of the protons in a nucleus plus the number of neutrons is called the mass number or A number. Elements with the same atomic number but a different mass number are called isotopes. The number of neutrons in the nucleus can be found by subtracting the Z number from the A number A-Z . Atoms and their isotopes are expressed by writing the A number over the Z number followed by the symbol of the element. 15O is oxygen 15 and 16O is oxygen 16. 8 8 You may notice on
