What is an atom? Try to come up with your own definition. Now turn to your partner and discuss.

Scientists who helped develop the atom! What did they do? Dalton J.J. Thomson Rutherford Bohr

* In the early 1800s, John Dalton performed experiments with gases. His results convinced him that matter was made up of tiny particles. …and that each element must be made of its own unique kind of particle and that these particles combine in simple ways. Dalton

dalton Dalton called these basic particles atoms and pictured them as tiny, spheres.

Dalton’s model All matter is composed of tiny, indivisible particles called atoms. Atoms of each element are exactly alike. Atoms of different elements have different masses. Atoms of different elements can join to form compounds.

At the end of the 1800s, J. J. Thomson discovered that atoms were not just simple, solid spheres and contained even smaller, subatomic particles. The subatomic particles Thomson discovered were very small and negatively charged. Thompson called them electrons. J.J. thomson

Thomson’s model “Plum Pudding Model” Thomson knew that atoms are electrically neutral. Therefore, he reasoned, an atom must contain enough positive charge to balance the negative charge of the electrons. Thomson developed an atomic model in which electrons were stuck into a positively charged sphere. A positive charge in the substance of the sphere balanced the electrons' charge . “Plum Pudding Model”

Rutherford His Model: His Experiment: MOST OF ATOM IS EMPTY SPACE!! After experimenting with a beam of positively charged light, he concluded that the protons are concentrated in a small area at the center of the atom. He called this region the nucleus. In his model, an atom is mostly empty space. The nucleus is tiny compared to the whole atom, but it contains nearly all the atom's mass. http://www.mhhe.com/physsci/chemistry/ess entialchemistry/flash/ruther14.swf

Bohr’s model He proposed that each electron in an atom has a fixed amount of energy. This energy keeps an electron moving around the nucleus within a specific region called an energy level. In Bohr's model, energy levels surround the nucleus in rings or shells, like the layers of an onion.

Electron cloud model Today scientists know that electrons do not actually orbit the nucleus as in Bohr's planetary model. The electron cloud model is now used to describe atoms. In this model, electrons dart about within an energy level in an ever-changing path. Most of this path falls into a region called an electron cloud. At any given time, there is a high probability that the electron exists in the electron cloud.

Atoms and elements Atoms are the building blocks of the universe. Scientists have identified nearly 100 different kinds of naturally occurring atoms. Each kind of atom has unique properties and is called an element. An atom of an element can't be broken down and retain its properties.

Particles inside an atom Inside the Nucleus: Center of the atom Neutrons- neutral charged particles Protons- positive charged particles Outside the Nucleus: Electrons- negatively charged particles

Check for understanding Fill in the chart about the 3 particles of the atom! Particle Charge Location Proton   Electron Neutron

Take a closer look… Atomic number: 11 Atomic mass: 22.990 Sodium contains 11 protons and 11 electrons! Atomic mass: 22.990 Mass number: 23 (rounded number) Number of Neutrons in Sodium: Mass number (23)-atomic number (11)= 12 neutrons

October 14th # __ POTASSIUM 2. PHOSPHORUS What is an atom? What are the 3 particles found in an atom? What are their charges? TAKE OUT YOUR PERIODIC TABLES AND IDENTIFY THE ATOMIC NUMBER AND ATOMIC MASS FOR EACH ELEMENT. HOW MANY PROTONS NEUTRONS AND ELECTRONS ARE IN EACH ELEMENT? POTASSIUM 2. PHOSPHORUS

October 15th # __ Take out your periodic table of elements. Find KRYPTON (Kr) How many protons: How many electrons: How many neutrons: (new number):