Atomic Structure Robert Erwin Science 8 UMS Rockwall ISD 2014 – 2015

Atomic Structure To understand how matter works, we need to understand what it’s made of – ATOMS. We use several tools to do so Models & numeric representations Scanning 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 Structure An Atom is divided into two areas: Nucleus Electron Cloud

Atomic Structure Within those two areas, the Atom is Made up of three main (sub-atomic) particles Nucleus Proton (+) positively charged Neutron (0) No Charge Electron Cloud Electron (-) Negatively charged Repeat this 3 times to your Neighbor.

Atomic Structure Protons and Neutrons are in the nucleus Electrons exist outside the nucleus in the electron cloud. The # of Protons = the # Electrons in a neutral atom.

Atomic Structure What 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 Structure Almost all of the mass of an atom is in its nucleus, made up of: Proton = 1 Atomic Mass Unit Neutron = 1 Atomic Mass Unit Electron Cloud has very little mass, made up of: Electron = 1/2000 th 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 -Protons Protons are in the nucleus Protons have a mass of 1 AMU The # 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 - Neutrons Neutrons are in the nucleus Neutrons have a mass of 1 AMU The # 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 - Electrons Electrons circle the nucleus in a cloud Electrons 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 – Variations An 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 We 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 Model The 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 1 st 18 elements fill in a pattern of 2, 8, 8.

Dimitri Mendeleev Russian 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