NCERT SCI-TEC IX Flashcards
International System of Units / SI
> > The modern SI system came into existence in 1875 with the TREATY OF METER
- mass kilogram Kg
- length meter m
- time seconds s
- electric current ampere A
- temperature kelvin K
- luminous Intencity candela cd
- amount of substance mole mol
All the other units are derived from these 7 units.
Define element, compound, & mixture.
An ELEMENT is a BASIC FORM OF MATTER that CANNOT BE BROKEN DOWN by chemical reaction INTO SIMPLER SUBSTANCES.
A COMPOUND is a SUBSTANCE COMPOSED OF TWO OR MORE DIFFERENT TYPES OF ELEMENTS chemically combined. Properties of compound are different from its constituent elements.
A MIXTURE contains MORE THAN ONE SUBSTANCE (elements & / or compounds) MIXED IN ANY PROPORTION.
Define solution, suspension, & colloid.
> > A SOLUTION is a HOMOGENOUS MIXTURE OF TWO OR MORE THAN TWO SUBSTANCES.
MAJOR COMPONENT of solution is called SOLVENT & MINNOR COMPONENT is called SOLUTE
> > SUSPENSION: Materials, INSOLUBLE in solvent, & of SMALLER PARTICLE SIZE but VISIBLE TO NAKED EYE, give SUSPENSION
> > COLLOIDS (e.g. fog, smoke etc) are HETEROGENEOUS MIXTURES where Particles called DISPERSED PHASE (~1000nm) are distributed throughout a solvent, called DISPERSING MEDIUM.
TYNDALL EFFECT: scattering of visible light passing through the dispersing medium [shafts of light coming through trees in the forest (is scattered by colloidal particles I.e. Fog, smoke]
Law of Conservation of Mass and Law of definite proportion
ANTOIN L. LAVOISIER laid the foundation of chemical sciences by establishing two important laws:
- LAW OF CONSERVATION OF MASS: states that MASS IS NEITHER CREATED NOR DESTROYED in a chemical reaction
- LAW OF CONSTANT PROPORTION: In a PURE CHEMICAL COMPOUND, ELEMENTS are always present IN DEFINITE PROPORTION BY MASS
Atom & atomic number
> > An atom is a SMALLEST PARTICLE OF AN ELEMENT WHICH CAN EXIST & RETAINS ALL THE CHEMICAL PROPERTIES OF THE ELEMENT. Atoms are NOT TRUELY INDIVISIBLE; they are themselves made up of particles (protons, neutrons, electrons, etc)
> 400 to 500 B.C. > Greek philosophers, Leuappus & Democritus > ATOM
500 B.C. > Indian philosopher Mahrshi Kanad > postulated PARMANU = Atom
> > Atomic number : The NUMBER OF PROTONS within the atom’s nucleus is called atomic number and is equal to the number of electrons in the neutral (non-ionized) atom.
Molecule
A molecule is a SMALLEST PARTICLE OF AN ELEMENT OR OF A COMPOUND, which can EXIST ALONE/FREELY under ordinary conditions & shows all properties of the substance. Similar to atoms, molecules also RETAIN THE CHEMICAL OF THAT SUBSTANCES (elements or compounds)
Define matter & substance.
Matter is anything that has MASS & OCCUPIES SPACE.
Classification:
1. PHYSICAL STATE as solid, liquid or gas, &
2. CHEMICAL CONSTITUTION as an element, compound or mixture
Substance is a KIND OF MATTER that CANNOT BE SEPARATED INTO OTHER KINDS OF MATTER by ANY PHYSICAL PROCESS.
How do scientists calculate atomic mass?
> Scientist use RELATIVE ATOMIC MASS SCALE to compare the masses of different atoms of elements.
Atoms of the isotope 12C are assigned the relative atomic mass of 12 & relative masses of all other atoms are obtained by comparison with the mass of a carbon-12 atom
Isotope
> Isotopes are VARIANTS of a particular chemical ELEMENT which DIFFER IN NEUTRON NUMBER, although all isotopes of a given element have the same number of protons in each atom. Each isotope of a given element has a different mass number. For example, carbon-12, carbon-13 and carbon-14 are three isotopes of the element carbon with mass numbers 12, 13 and 14 respectively.
> The term isotope is formed from the Greek roots isos (ἴσος “equal”) and topos (τόπος “place”), meaning “the same place”. Thus, different isotopes of a single element occupy the same position on the periodic table.
> The NUMBER OF PROTONS within the atom’s nucleus is called ATOMIC NUMBER and is equal to the number of electrons in the neutral (non-ionized) atom.
> Each atomic number identifies a specific element, but not the isotope; an atom of a given element may have a wide range in its number of neutrons. The NUMBER OF NUCLEONS (both protons and neutrons) in the nucleus is the ATOM’S MASS NUMBER, and each isotope of a given element has a different mass number.
Mole & molar mass
> > The mole is the AMOUNT OF SUBSTANCE, which contains the SMAE NUMBER OF PARTICLES (atoms, ions, molecules or formula units) AS THERE ARE ATOMS IN EXACTLY 12g of 12C
> > Mass of ONE MOLE MOLECULES of a substance is its MOLAR MASS
What is an empirical formula & a molecular formula?
> > An empirical formula shows the SIMPLEST WHOLE NUMBER RATIO OF THE ATOMS OF DIFFERENT ELEMENTS PRESENT IN A COMPOUND
> > A molecular formula shows the ACTUAL NUMBER OF ATOMS OF DIFFERENT ELEMENTS IN THE ONE MOLECULE OF A COMPOUND
In India which institution realises the base units & maintains the National Standards of Measurements?
In India NATIONAL PHYSICS LABORATORY (NPL), New Delhi, realises the base units & maintains the national standards of measurements
> All measurements made in the country are linked to the national standards
> The NPL ensures that the Indian National Standards meet all our requirements & are equivalent to the International Standards
Which institution in India maintains the standards of the ionising radiations?
BHABHA ATOMIC RESEARCH CENTRE, MUMBAI
