Introduction to the Atom Structure of Matter Each of the more than 100 elements of matter has distinct properties and a distinct atomic structure. All forms of matter are composed of one or more of the elements. Students know the structure of the atom and know it is composed of protons, neutrons, and electrons. Students know that compounds are formed by combining two or more different elements and that compounds have properties that are different from their constituent elements. Students know atoms and molecules form solids by building up repeating patterns, such as the crystal structure of NaCl or long- chain polymers. Students know the states of matter (solid, liquid, gas) depend on molecular motion. Students know that in solids the atoms are closely locked in position and can only vibrate; in liquids the atoms and molecules are more loosely connected and can collide with and move past one another; and in gases the atoms and molecules are free to move independently, colliding frequently. Students know how to use the periodic table to identify elements in simple compounds. Chapter 4 Section 1

What is an Atom. The smallest particle from which all element are made What is an Atom? The smallest particle from which all element are made. All matter is composed of atoms. Neutrons Neutrally charged particles in an atom’s nucleus Protons Positively charged particle in an atom’s nucleus Electrons Negatively charged particles in a cloud-like region that surrounds the nucleus of the atom.

Thomson’s Model 1904 “Plum Pudding” Scientists knew that atoms contained no charge, but the particles within an atom do! 1897 – Electron discovered Negatively charged “plums” in a “pudding” of positive charge.

Rutherford’s Model 1911 “Planetary Model” Gold Foil Experiment http://www.pearsonsuccessnet.com/snpapp/iText/products/0-13-203527-8/phs_ca_sci_gr8_main.html What did it prove? Nucleus! The bulk of the mass of the atom was in the center.

Rutherford’s Model 1911 “Planetary Model” Nucleus: The central core of the atom, composed of protons and neutrons Electrons circle the nucleus like planets around the sun.

Bohr’s Model 1913 “Onion Model” The electrons circle the nucleus in orbits of specific energy levels, like the layers of an onion. At this point, we still had not discovered neutrons. The nucleus was just a positive mass.

Energy Levels Electrons of different energy levels are located at different locations around nucleus Level 1 = Holds up to 2 e- Level 2 = Holds up to 8 e- Level 3 = Holds up to 8 e-

Modern Atomic Model 1932 “Cloud Model” Electrons are not just limited to orbits, but freely roam in a cloud around the nucleus. Energy levels determine how much an electron moves. And. . . We discovered neutrons!

5 Minute Free-Draw! Use the whiteboard tools to draw your own version of each scientists’ model: Thomson’s Model: Rutherford Model: Bohr’s Model: Modern Model:

Structure of an Atom Atomic Number The number of protons in the nucleus of an atom Elements are identified by their atomic number. Every atom of a given element has the same number of protons. # Protons = # Electrons

Mass Number Mass Number the sum of the protons and neutrons in an atom Where is most of the mass of an atom located? ________ and ________ make up most of the mass. The are equal in mass. __________ are much smaller, 1,836 times smaller!

Mass Number We can calculate the number of neutrons, using the atomic number and mass number. This element is Nitrogen. Its mass is 14. Its Atomic Number is 7. Mass Number = neutrons + protons So, we have _____ neutrons.

What is the Atomic Number? Why is the Mass Number 12?

Atoms of the same element that have different numbers of neutrons. Isotopes Atoms of the same element that have different numbers of neutrons. Do you think Isotopes of the same element have different mass numbers? Do they have different atomic numbers?