# Atomic Structure lecture 4.1. Atomic structure Small, dense nucleus Protons: (+) charge Neutrons : (0) no charge Electrons: (-) charge # Protons = # electrons.

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Atomic Structure lecture 4.1

Atomic structure Small, dense nucleus Protons: (+) charge Neutrons : (0) no charge Electrons: (-) charge # Protons = # electrons Electrically neutral, as + and – charges are equal

Particle sizes Almost all the mass is in the nucleus ( Protons + Neutrons ) Electrons move in a cloud around the nucleus If the nucleus was the size of a marble, the electron cloud would be the size of a stadium!

Energy levels Electrons fill up orbitals around the nucleus Each level holds only so many electrons Level 1- holds 2 Level 2 – holds 8 Level 3 – holds 18 Left side: If an atom had its first 2 orbitals filled how many electrons and protons would it have?

Valence electrons the electrons on the outermost level are called valence electrons, determine reactivitythe electrons on the outermost level are called valence electrons, determine reactivity Reactivity is how likely an atom is to form bonds with another elementReactivity is how likely an atom is to form bonds with another element Left side: How many valence electrons do Ar and H have?

Isotopes Isotopes are variations of the same element Isotopes are variations of the same element – The proton number is always the same, but the number of neutrons can change – They have a different atomic mass. The greater the number of neutrons the greater the mass

Calculating neutrons Mass # – atomic # = # neutrons Average atomic mass : Numbers are the average masses of all the isotopes of the element

Summary Review 1.What are the 3 subatomic particles, their charge, and location? 2. If an element has 2 protons how many electrons does it have? 3. The electrons in the outermost energy level are called ____________ electrons. 4. What is an isotope and what is atomic mass?

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