Atomic Structure

Robert Erwin Science 8UMS Rockwall ISD2014 – 2015

Atomic StructureTo understand how matter works, we need to

understand what it’s made of – ATOMS.We use several tools to do so

Models & numeric representationsScanning tunneling microscopes

An Atom is the smallest unit of an element.Turn to your neighbor and repeat 5 times“An Atom is the smallest unit of an element”.“Atoms are the building blocks of matter”.

Atomic StructureAn Atom is divided into two areas:

Nucleus

Electron Cloud

Atomic StructureWithin those two areas, the Atom is Made up of

three main (sub-atomic) particlesNucleus

Proton (+) positively chargedNeutron (0) No Charge

Electron CloudElectron (-) Negatively chargedRepeat this 3 times to your

Neighbor.

Atomic StructureProtons and Neutrons are in the nucleusElectrons exist outside the nucleus in the

electron cloud.The # of Protons = the # Electrons in a

neutral atom.

Atomic StructureWhat is the smallest unit of an element?What is the building block of all matter?What are the two areas of an atom?What are the three sub-atomic particles?Where do we find each?What are their electrical charges? Repeat this 3 times to your neighbor.

Atomic StructureAlmost all of the mass of an atom is in its

nucleus, made up of:Proton = 1 Atomic Mass UnitNeutron = 1 Atomic Mass Unit

Electron Cloud has very little mass, made up of: Electron = 1/2000th Atomic Mass Unit

Add the Protons and Neutrons to get the Atomic Mass. Omit the electrons, as they don’t have enough

mass to calculate at this level.

Atomic Structure -ProtonsProtons are in the nucleusProtons have a mass of 1 AMUThe # of Protons in an atom

determine what element it is. (Ex: If an atom has exactly 3 protons, it is ALWAYS Lithium)

The # of Protons in an atom is also = its Atomic Number.

Atomic Structure - NeutronsNeutrons are in the nucleusNeutrons have a mass of 1 AMUThe # of Neutrons will often be close to the

# of Protons – but not always exactly the same. (Ex: Lithium has 3 Protons but 4 Neutrons)

Atomic Structure - ElectronsElectrons circle the nucleus in a cloudElectrons have a mass of 1/2000

th AMU

The # of Electrons will = the # of Protons in a neutral atom. (Ex: Lithium has 3 Protons and 3 electrons)

Valence Electrons are the outermost electrons.

Valence Electrons determine an atom’s reactivity (how it behaves).

Atomic Structure – VariationsAn Ion is an atom where the # of

Protons does not = the # of Electrons.An atom with fewer electrons has a

positive charge (+).An atom with more electrons has a

negative charge (-).An Isotope is an atom that has

more or fewer Neutrons, so has a different mass than the average balanced atom.

Niels Bohr - 1913We use his model to understand basic

atomic structure. We do not think that this is what an atom

actually looks like It is a useful tool to help us understand

atomic concepts

Bohr ModelThe Bohr model looked like a tiny solar system

The nucleus was represented in the center, like a star

The paths of the electrons looked like planets orbiting around the star.

Electrons orbit at different distances (Shells) from the nucleus due to different energy levels they hold

Each electron shell has a maximum number of electrons it can hold

The electron shells of the 1st 18 elements fill in a pattern of 2, 8, 8.

Dimitri Mendeleev - 1869Russian scientist who

categorized the known elements.

Accurately predicted elements that had not yet been discovered.

Created the modern Periodic Table of the Elements.

Rephrased – TV Sitcom WKRP• Station DJ mentor teaching local gang member about atomic structure

• Made a bet with him to get him to stay in school• What will take for you? If you don’t get it – let someone know. • There are LOTS of ways to learn• http://www.youtube.com/watch?v=hhbqIJZ8wCM