3. Atom Characteristics All matter (stuff with mass and volume) is made of atoms. Space (without any particles) has no atoms. Atoms are made of smaller particles : protons (+), neutrons ( ), and electrons (-). Protons, neutrons, and electrons, of course, are made of even smaller particles…

5. Atomic Size Atoms are unbelievably tiny. How tiny? Incredibly smaller than plant and animal cells. Billions of atoms make up the writing tip of your pen or pencil.

6. A key discovery leading to the current model of the atom was that atoms contain charged particles. The charge on a particle can be either positive or negative. Particles with the same type of charge repel each other—they are pushed apart. Particles with different charges attract each other—they are drawn toward each other.

7. The neutron has approximately the same mass as a proton.

9. Review Time!!!!!! The protons and neutrons of an atom are grouped together in the atom’s center. This combination of protons and neutrons is called the nucleus of the atom. Because it contains protons, the nucleus has a positive charge. Electrons are negatively charged particles that move around outside the nucleus.

10. Atomic Numbers If all atoms are composed of the same particles, how can there be more than 100 different elements? The identity of an atom is determined by the number of protons in its nucleus, called the atomic number. Every hydrogen atom—atomic number 1—has exactly one proton in its nucleus. Every gold atom has 79 protons, which means the atomic number of gold is 79.

11. The number of protons present in the nucleus of an atom of an element is known as its atomic number. The total number of protons and neutrons in the nucleus of an atom of an element is known as its mass number. Atomic Number and Mass Number.

12. Atomic Mass Number The total number of protons and neutrons in an atom’s nucleus is called its atomic mass number. While the atoms of a certain element always have the same number of protons, they may not always have the same number of neutrons, so not all atoms of an element have the same atomic mass number.

13. Isotopes Atoms of the same element can be different (they can have different # of neutrons) –Thus, different mass numbers. These are called isotopes.

14. Isotopes are atoms of the same element having different masses, due to varying numbers of neutrons.

15. IsotopeProtonsElectronsNeutronsNucleus Hydrogen–1 (protium) 110 Hydrogen-2 (deuterium) 111 Hydrogen-3 (tritium) 112