Elements and Atoms

1. Elements and Atoms

2. Elements • Elements are natter that cannot be broken down into other substance by any other chemical means • Elements are considered pure substances because it is made of only one kind of matter and has definite properties

3. Atoms • Elements are made of atoms. Much like all of the pixels on a TV screen make up the picture we see. Very small particles make up elements and those particles are called atoms. • An atom is the smallest particle of an elements. The atom of each element has a very specific structure.

4. Atomic Structure • An atom is composed of three different subatomic particles called the proton, neutron and electron • The nucleus is the center of the atom and it holds the protons which have a positive charge (+)and the neutrons which have a neutral charge(0). • Around the outside of the nucleus spinning in a variety of energy levels are the third particle. The electron that has a negative charge (-)

5. Atomic Models • To understand elements interact with one another we have to understand how they are built. • Over the years there have been many different models of how scientists think atom may be structured. There was the Dalton Model (1808), Thomson Model (1897), Nagaoka Model (1900), Rutherford Model (1911), Bohr Model (1913), Chadwick Model (1932), Modern Model (1920), Revised Bohr Model

6. Bohr Model • Electrons could only occupy certain orbits (usually referred to as energy levels or shells) around the nucleus. They also discovered that only a certain number of electrons could fit in each energy level. • To properly place the electrons around the nucleus, you will need to refer to your element's electron configuration table • In the Bohr model, a nitrogen atom has a central nucleus, composed of seven protons and seven neutrons, surrounded by seven electrons. Two of the electrons are in the first energy level while the other five are in the second energy level.

7. According to nitrogen's electron configuration table, an atom of nitrogen contains two electrons in its first energy level and five electrons in its second energy level. A Bohr model of a nitrogen atom could look like this:

8. Revised Bohr Model • Further studies showed that the Bohr model wasn't as accurate as it could be. Scientists learned that each energy level is made from a certain number of sub-shells. The sub-shells, which are named s, p, d and f, can each hold only a certain number of electrons. The s sub-shell can only hold 2 electrons, the p sub-shell can hold 6, the d sub-shell can hold 10 and the f sub-shell can hold 14. The number of available sub-shells increases as the energy level increases. • To properly place the electrons around the nucleus, you will need to refer to your element's electron configuration table. • In the refined Bohr model, a nitrogen atom has a central nucleus, composed of seven protons and seven neutrons, surrounded by seven electrons. Two of the electrons are in the s sub-shell of the first energy level, two are in the s sub-shell of the second energy level and three are in the p sub-shell of the second energy level.

9. According to nitrogen's electron configuration table, an atom of nitrogen contains two electrons in its first energy level (both in the s sub-shell) and five electrons in its second energy level (two in the s sub-shell and three in the p sub-shell). A more accurate Bohr model of a nitrogen atom could look like this:

10. SO How do we make models of atoms? • Select an element to make a model of • Look at the elements atomic number (which is the number of protons) • Draw the nucleus in the center of the atom and place the number of protons in the nucleus that are indicated by the atomic number. The number of protons and neutrons is generally the same so you can also draw in the neutrons.

11. Lets pick the element Hydrogen • Hydrogen has an atomic number of 1, so it would have one proton and one neutron in the nucleus. Neutron (neutral) 0 + Proton (positive)

12. By definition atoms have no charge so if there is one proton then there must be one electron to balance the charges. • But where do the electrons go? To add in the electrons we need to understand the energy levels • There are six different energy levels that electrons can exist in. • There are only a certain number of electrons that can be in each level. We often call these energy levels shells. • The shells also need be broken into sub shells because electrons need so much space that they must have a defined area in the atom. The next slide shows the break down of shells and sub-shells

14. So lets go back to our model of Hydrogen. Hydrogen has one proton so it must also have only one electron. • The one electron would be located in the lowest energy level 1 in the s sub-shell. - 0 0 +

15. Electron Configuration • To figure out where the electrons will go is pretty simple for an element like hydrogen, but as the number of electrons increase it becomes pretty difficult. So chemist use electron configuration to show which shells and sub-shells the electrons are located in. • Electron configuration is like a sentence that explain in which shell and sub-shell is each electron is located. The sub-shell The energy level/shell Number of electrons in the sub-shell

16. The electron configuration for hydrogen would be 1s1 • The next element helium which has an atomic number of 2 would have a configuration of 1s2 . • The element lithium has the atomic number of 3 and would have an electron configuration of 1s2 2s1 • The element beryllium has an atomic number of four so it electron configuration would be: 1s2 2s2

17. How would the atomic models of helium, lithium and beryllium look?