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Aim: What are the Parts of an Atom? 0 Rings • Electrons 0 0 0 Nucleus • Protons • Nuetrons ! ! ! Particles that are smaller than the atom are called subatomic particles. The three main subatomic particles that form an atom are protons, neutrons, and electrons. The center of the atom is called the nucleus. ! ! ! ! Protons and neutrons make up the nucleus of an atom. All protons are identical to each other, and all neutrons are identical to each other. Protons have a positive electrical charge, so they are often represented with the mark of a "+" sign. Neutrons have no electrical charge and are said to help hold the protons together (protons are positively charged particles and should repel each other). ! ! If all protons are identical and all neutrons are identical, then what makes the atoms of two different elements different from each other? For example, what makes a hydrogen atom different from a helium atom? ! The number of protons and neutrons in the nucleus give the atoms their specific characteristics. ! The atomic nucleus is the densest part of any atom. It is the area that contains the protons and neutrons. In most atoms the nucleus accounts for over 99% of the atom’s mass. ! Nucleus has a large mass " " Protons and neutrons Nucleus has a small volume Large Mass = Very Dense! Small Volume ! Rings have a small mass " ! Electrons Rings have a large volume " Mostly empty space Small Mass = Not Dense Large Volume Electrons are the negatively charged particles of atom. Together, all of the electrons of an atom create a negative charge that balances the positive charge of the protons in the atomic nucleus. ! Electrons are extremely small compared to all of the other parts of the atom. The mass of an electron is almost 1,000 times smaller than the mass of a proton ! Electrons are found in clouds that surround the nucleus of an atom. Those clouds are specific distances away from the nucleus and are generally organized into shells. Because electrons move so quickly, it is impossible to see where they are at a specific moment in time. ! After years of experimentation, scientists discovered specific areas where electrons are likely to be found. The overall shape of the shells changes depending on how many electrons an element has. The higher the atomic number, the more shells and electrons an atom will have. ! The closer an electron is to the nucleus, the greater the attractive force. Hence electrons bound near the center of the atom require more energy to escape than those at greater separations.