ATOMS, ELEMENTS, COMPOUNDS AND MIXTURES….. SEC 1 MODELS OF ATOM CHAPTER 1 ATOMS, ELEMENTS, COMPOUNDS AND MIXTURES….. SEC 1 MODELS OF ATOM
THE STUDENTS WILL: Explain how scientists discovered subatomic particles. Explain how today’s model of the atom developed. Describe the structure of the nuclear atom.
Terms to Know: Atoms Element Electrons Protons Neutron Electron cloud
What is an Element? A substance that cannot be broken down into simpler substances is called an element. Ex. Gold (Periodic Table of Element)
WHO ARE THESE MEN? In this lesson, we’ll learn about the men whose quests for knowledge about the fundamental nature of the universe helped define our views.
What is an Atom? - “ATOMOS” Greek name- means uncuttable or something that cannot be divided further -A basic unit of matter - All matter is made up of atoms.
History of Atom…. Democritus developed the idea of atoms. 460 BC He pounded up materials in his pestle and mortar until he had reduced them to smaller and smaller particles which he called ATOMA 460 BC
2. JOHN DALTON -suggested that all matter was made up of tiny spheres that were able to bounce around with perfect elasticity and called them ATOMS 1808
DALTON’S CONCEPT OF ATOMS Matter is made up of Atoms. Atoms cannot be divided into smaller pieces. All the atoms of an element are exactly alike. Different elements are made up of different kinds of atom
William Crooke Cathode Ray Tube (CRT) 1870 Experimented with a Glass Tube using Electrodes Cathode Ray Tube (CRT)
Crooke hypothesized that: the green glow inside the tube was caused by rays or streams of particles….called cathode rays.
3. JOSEPH JOHN THOMPSON 1898 -English Physicist Repeated Crooke’s Experiment Cathode Rays are negatively charged 1898
THOMSON’S MODEL Thomson studied the passage of an electric current through a gas. As the current passed through the gas, it gave off rays of negatively charged particles.
Where did they come from? This surprised Thomson, because the atoms of the gas were uncharged. Where had the negative charges come from?
Thomson concluded that the negative charges came from within the atom. A particle smaller than an atom had to exist. The atom was divisible!
But he could never find them. ` Thomson called the negatively charged “corpuscles,” today known as electrons. Since the gas was known to be neutral, having no charge, he reasoned that there must be positively charged particles in the atom. But he could never find them.
4. Ernest Rutherford Atoms are mostly empty space. Negative electrons orbit a positive nucleus. 1910
Rutherford’s experiment Involved firing a stream of tiny positively charged particles at a thin sheet of gold foil…. -
Most of the positively charged “bullets” passed right through the gold atoms in the sheet of gold foil without changing course at all. Some of the positively charged “bullets,” however, did bounce away from the gold sheet as if they had hit something solid. He knew that positive charges repel positive charges.
Rutherford’s new evidence allowed him to propose a more detailed model with a central nucleus. He suggested that the positive charge was all in a central nucleus. With this holding the electrons in place by electrical attraction
Parts of an ATOM: PROTONS- positively charged particles inside the nucleus of an atom. ELECTRONS- negatively charged particles moving around the nucleus. NEUTRONS- neutral charge (same mass as the protons)inside the nucleus.
ELECTRON CLOUD Area around the nucleus of an atom where electrons travel.
Atomic Model