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Atomic Structure and the Periodic Table Chapter 2-1.

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Presentation on theme: "Atomic Structure and the Periodic Table Chapter 2-1."— Presentation transcript:

1 Atomic Structure and the Periodic Table Chapter 2-1

2 Chemical symbols Abbreviated way to write the name of an element Always starts with a capital letter If double letters – first is capitalized second is lower case Cl Ar Ne

3 atom Smallest part of matter Basic building block of matter Parts of an atom – Nucleus – center – – protons - + charge – neutrons - neutral charge size: mass p = mass n

4 Electron cloud – Surrounds the nucleus – Contains electrons – Electrons have a negative charge – Size: mass e = 1/2000 of m p – mass so tiny that it isn’t even considered in the mass of an atom – Moves around the nucleus at such speeds that they cannot be seen. – Cloud like appearance

5 – Neutral atom – the number of positive charges equal the number of negative charges – All elements on periodic table are stable atoms.

6 Atomic number Number of protons in an atom Every atom of the same element has the same atomic number Identity number of an element

7 Danish scientist Neils Bohr 1913 Developed the first model of what the atom looks like

8 Bohr diagram Central nucleus Electrons moving around it in well defined paths or orbits.

9 Electron clouds Electrons moving so fast that they cannot be seen Electrons move within a certain region NOT on orbits

10 Energy Levels and Electrons Electrons are at varying distances from nucleus – e near nucleus – low energy – e farther from nucleus – high energy

11 Energy levels – Each holds a different amount of electrons – There is a maximum number of electrons each can hold

12 1 st 2 e 2 nd 8 e 3 rd 18 e 4 th 32 e

13 Mass number – Number of protons + neutrons in nucleus

14 Number of Neutrons Mass number - # p = #n

15 Isotopes Atoms of the same element that have a different number of neutrons Average atomic mass – average mass of an element and its isotopes Written H-1 H-2 H-3 element – mass #




19 Isotopes of hydrogen H-1 protium H-2 deuterium H-3 tritium

20 Importance of Isotopes Used in: Medical field – radioactive to detect cancers, thyroid disorders Dating – to date age of rocks or artifacts Radioactive power plants

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