Elements and Atoms ch.1 Flashcards
What is an element?
They are the simplest pure substances. They cannot be broken down to any other substance.
Why are elements sometimes called the building blocks of matter?
…..because all matter is composed of one element or a combination of two or more elements.
What is a compound?
A pure substance made of two or more elements that are combined CHEMICALLY with a specific ratio
ex. Salt (sodium chloride)
What is a mixture?
It is two or more substances that are in the same place but are NOT chemically combined.
ex. air, soil, wood, orange juice
What is an ATOM?
- It is the smallest particle of an element.
- Consists of a small, positively charged nucleus
- most of the volume contains protons and neutrons
- no overall electrical charge because it has the same amount of electrons as protons.
- It is surrounded by a cloud like region of negatively charged electrons.
What is Scientific Theory?
It is a well-tested idea that explains and connects a wide range of observations.
Why do scientists use MODELS to help them understand atoms?
Models are physical or other representations of an idea that helps scientists to understand what cannot be observed directly.
What is the timeline of the Atomic Theory? How did it grow and change?
- 430 b.c. DEMOCRITUS - invented the idea of the atom.
- 1800’s DALTON - proposed one of the 1st models of the atom;pool balls.
- 1897 J.J. THOMPSON - discovered that atoms contain negatively charged particles; electrons, scattered through a ball of positive charge.
- 1911 RUTHERFORD - introduced the motion of the electrons and PROTONS exist in the nucleus. Experiment: Rutherford Gold Foil
- 1913 BOHR - electrons move around the nucleus in certain orbits.
- 1932 CHADWICK - discovered the neutron.
What is energy level?
A region where electrons of the SAME energy are likely to be found.
What is a nucleus?
a positive region in the center of an atom.
What is a proton?
positively charged particles in the center of the nucleus.
What are neutrons?
a particle in the neutron that is electrically neutral.
What are electrons?
The negatively charged particles surrounding the nucleus.
Describe \john Dalton’s atomic theory.
- all elements are composed of atoms
- an atom of one element cannot be changed into an atom of a different element.
- atoms cannot be created or destroyed in any chemical changes.
- every compound is composed of atoms of different elements.
Is the Dalton’s atomic theory accepted today?
Yes
