Atoms, Element, Molecule and Compound

Physical Science Grade 11 or 12 ABM Strand K-12 Senior High School (Curriculum Guided)

1. Atoms, Element, Molecule and Compound

2. Atom the basic unit of a chemical element. Atoms  are the basic building blocks of element and matter. An   atom  itself is made up of three tiny kinds of particles called subatomic particles: protons, neutrons, and electrons .

3. Helium A  helium atom  is an  atom  of the chemical element  helium .  Helium  is composed of two electrons ,two protons along with one neutron.

4. Element An element is a substance that is made entirely from one type of atom.

5. For example, the element  hydrogen  is made from atoms containing a single   proton  and a single  electron . (If you change the number of protons an atom has, you change the type of element it is .)

6. Molecule Molecules  form when two or more atoms form chemical bonds with each other . Molecules form when two or more atoms form chemical bonds with each other. It doesn't matter if the atoms are the same or are different from each other.

7. Single atoms  of elements are not molecules. A single oxygen, O, is not a molecule. When oxygen bonds to itself (e.g., O 2 , O 3 ) or to another element (e.g.,  carbon dioxide or CO 2 ), molecules are formed.

8. EXAMPLES OF MOLECULES Molecules may be simple or complex. Here are examples of common molecules: H2O (water) N2 (nitrogen) O3 (ozone) CaO (calcium oxide) C6H12O6 (glucose, a type of sugar)

9. Compound A compound is a molecule that contains at least two different  elements . 

10. Examples Water (H 2 O), carbon dioxide (CO 2 ) and methane (CH 4 ) are compounds.

11. All compounds are molecules but not all molecules are compounds.

12. Molecular  hydrogen  (H 2 ), molecular  oxygen  (O 2 ) and molecular  nitrogen  (N 2 ) are not compounds because each is composed of a single element.

13. Water (H 2 O), carbon dioxide (CO 2 ) and methane (CH 4 ) are compounds because each is made from more than one element. 

14. Is H 2 O a Molecule or a Compound?

15. Subatomic Particles Proton(p) positive (+) charge Electron( e −) negative (-) charge Neutron (n) No charge; neutral

16. How to determine the number of protons? The  number of protons  in the nucleus of the atom is equal to the  atomic number ( Z ) p=atomic number(Z)

17. How to determine the number of electrons? The  number  of electrons in a neutral atom is equal to the  number of protons e −=p/atomic number(Z)

18. Example Helium : Atomic number(Z)= 2 Protons = 2 Electron = 2

19. How to determine the number of neutrons? The number of neutrons is equal to the difference between the mass number of the atom ( A ) and the atomic number ( Z ). number of neutrons (n )= Mass number (A) – Atomic Number (Z)

20. Mass number/atomic weight The mass number of the atom ( A ) is equal to the sum of the number of protons and neutrons in an atom. (A) mass number = atomic number (Z) + Neutron

21. Helium : Atomic number(Z)= 2 Protons = 2 Electron = 2 Atomic Mass = 4.002602 (4) A (4) – Z (2) = 2 (n) Neutron = 2

22. Element Number of Protons Number of Electrons Number of Neutrons Atomic Number Mass Number 19 20 19 Cs 55 133 79 118 Mg 12 12

23. Element Number of Protons Number of Electrons Number of Neutrons Atomic Number Mass Number K 19 19 20 19 39 Cs 55 55 78 55 133 Au 79 79 118 79 197 Mg 12 12 12 12 24