Introduction to the Atoms

How would it feel to discover something you can’t see? “A scientist may feel frustrated that we know that we have found or discovered something, but we can’t visualize it.”

History of the Atom Ancient Greeks believed that matter is made up of smaller parts that cannot be broken down Atoms smallest particle that an element can be divided into. Atoms comes from the Greek word atomos which means “indivicible.” Atoms are made up of even smaller particles called protons, neutrons, & electrons. Protons & neutrons stick together to form the nucleus, which is the center of the atom. Electrons are located surrounding the nucleus in the electron cloud.

Dalton’s Atomic Theory All elements are made up of atoms. Atoms of the same element have the same mass. An atom of one element cannot be changed into a atom of a different element. Every compound is made of elements that follow the same recipe or ratio.

John Dalton’s Atomic Theory Questions 1-4: Read each part of John Dalton’s Atomic Theory and match the part of the theory with the explanation. John Dalton’s Atomic Theory Explanation of Theory 1. All elements are made of atoms that cannot be divided or broken down into smaller parts. A. An atom of gold could never be an atom of silver. 2. All atoms of the same element have the same mass. B. Elements will always follow a pattern when combining together. 3. An atom of one element cannot be changed into an atom of a different element. C. Atoms are the smallest part of matter. 4. Compound are made of different elements in a specific ratio. D. All atoms of an element will weigh the same.

Atoms are composed of three types of subatomic particles Symbol Charge Location Protons p+ Positive charge Found in the nucleus Neutrons N0 Neutral (no) charge Electrons e- Negative charge Found orbiting the nucleus

Important Scientist John Dalton proposed that all substances are made up of atoms. These atoms are small dense spheres that cannot be created or destroyed. J.J Thompson proposed that atoms were made up of small particles called protons (+) & electrons (-). However J.J did not know where the p+ or e- where located. He thought they we are evenly distribute Earnest Rutherford proposed that an atom had a dense positively charged nucleus surrounded by electrons (-) Niels Bohr 2 years after Rutherford proposed his theory Bohr stated that electrons revolved around the nucleus in circular paths called ORBITS. Bohr also stated that there could only be a certain amount of electrons in each orbit.

Thomson’s Model Believed that the atom was like a chocolate chip muffin Cake= positive charged area Chips = electrons Discovered the Electron

Rutherford’s Model Positive charge lies within a center called the nucleus Electrons moved around this nucleus Discovered the Proton

Bohr’s Model Proposed that electrons only have enough energy to travel around the nucleus in a set pattern like the planets around the sun

Modern Model Chadwick’s discovery of the neutron led to scientists fixing the model Nucleus: protons & neutrons Electron Cloud: electrons that in a range of space, no exact location

BOHR MODEL Calculating the # of electrons in each shell In other words, electron shells have a limited capacity for electrons.  As you might expect, the farther an electron shell is from the nucleus, the larger it is.  You can calculate the total capacity of an electron shell using the formula 2n2, where n equals the number of the electron shell.  For example, for the 1st electron shell n = 1 and 2 x 1x1 = 2, telling us that the capacity of the 1st shell is 2 electrons as we have already seen.  For the 2nd shell (n = 2) and 2 x 2x2 = 8.  For an atom to fill its 2nd electron shell, it would need 10 electrons: 2 to fill the 1st shell and 8 to fill the 2nd.  The 3rd shell has a total capacity of 2 x 3x3 = 18 electrons.

Orbitals Maximum Number of Electrons in the Shell 1 2 x (1 x 1) = 2 Shell Number 2 * (the shell number   * the shell number) = the maximum number of electrons in this shell.  Maximum Number of Electrons in the Shell 1 2 x (1 x 1) = 2 2 x 1 = 2 2 2 x (2 x 2) = 8 2 x 4 = 8 3 2 x ( 3 x 3) = 18 2 x 9 = 18 4 2 x (4 x  4) = 32 2 x 16 = 32 5 2 x (5 x 5) = 50 2 x 25 = 50 Orbitals There are five possible shells available to atoms.  This diagram shows only three shells, and some atoms, such as the little hydrogen atom, use only the one inner shell.      Each of the elements has a different number of the tiny electrons, and a corresponding number of protons. Hydrogen is the smallest, with only one electron. Carbon, nitrogen, and oxygen, are also small, light atoms.

Bohr Model problems: Do the Bohr model for each one of the elements stated below. Element name Number of Electrons 1. Carbon 4 2. Neon 10 3. Sodium 11 4. Calcium 20 5. Lithium 3 6. Hydrogen 1

Sample Isotopes of Hydrogen & Carbon Protons + neutrons # of protons